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Internet-Draft Grenville Armitage
Bellcore
May 31st,
August 11th, 1995
Support for Multicast over UNI 3.1 based ATM Networks.
<draft-ietf-ipatm-ipmc-05.txt>
<draft-ietf-ipatm-ipmc-06.txt>
Status of this Memo
This document was submitted to the IETF IP over ATM WG. Publication
of this document does not imply acceptance by the IP over ATM WG of
any ideas expressed within. Comments should be submitted to the ip-
atm@matmos.hpl.hp.com mailing list.
Distribution of this memo is unlimited.
This memo is an internet draft. Internet Drafts are working documents
of the Internet Engineering Task Force (IETF), its Areas, and its
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Please check the lid-abstracts.txt listing contained in the
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Internet Draft.
Abstract
Mapping the connectionless IP multicast service over the connection
oriented ATM services provided by UNI 3.1 is a non-trivial task. This
memo describes a mechanism to support the multicast needs of Layer 3
protocols in general, and describes its application to IP
multicasting in particular.
ATM based IP hosts and routers use a Multicast Address Resolution
Server (MARS) to support RFC 1112 style Level 2 IP multicast over the
ATM Forum's UNI 3.1 point to multipoint connection service. A single
endpoint interface behaviour is described, along with two levels Clusters
of endpoints share a MARS - Class I and Class II. The Class I MARS service supports layer use it to track and disseminate
information identifying the nodes listed as receivers for given
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multicast groups. This allows endpoints to establish and manage point
to multipoint VCs when transmitting to the group.
The MARS behaviour allows Layer 3 multicasting to be supported using
either meshes of VCs. The Class II MARS adds the
ability to use VCs or ATM level multicast servers to support distribution of
layer 3 packets.
[Editorial note: servers. This version has been substantially restructured
from ipmc-04 in an attempt to group related topics together in choice may
be made on a
more logical fashion. Additions and modifications to the actual
protocol are generally in accordance with the set of proposed
changes published per-group basis, and updated during the March to May time period.
Section 5.4 is a notable exception to this, and transparent to a lesser extent
so is section 5.3. Other tweaks were added as inspiration took me
during the rewrite session.] endpoints.
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Contents.
1. Introduction.
1.1 The Multicast Address Resolution Server (MARS).
1.2 The ATM level multicast Cluster.
1.3 Document overview.
1.4 Conventions.
2. The IP multicast service model.
3. UNI 3.1 support for intra-cluster multicasting.
3.1 VC meshes.
3.2 Multicast Servers.
3.3 Tradeoffs.
3.4 Interaction with local UNI 3.1 signalling entity.
4. Overview of the MARS.
4.1 Architecture.
4.2 Control message format.
4.3 Common header values in MARS messages.
5. Endpoint (MARS client) interface behaviour.
5.1 Transmit side behaviour.
5.1.1 Retrieving Group Membership from the MARS.
5.1.2 MARS_REQUEST, MARS_MULTI, and MARS_NAK messages.
5.1.3 Establishing the outgoing multipoint VC.
5.1.4 Monitoring updates on ClusterControlVC.
5.1.4.1 Updating the active VCs.
5.1.4.2 Tracking the Cluster Sequence Number.
5.1.5 Revalidating a VC's leaf nodes.
5.1.5.1 When leaf node drops itself.
5.1.5.2 When a jump is detected in the CSN.
5.2. Receive side behaviour.
5.2.1 Format of the MARS_JOIN and MARS_LEAVE Messages.
5.2.1.1 Important IPv4 default values.
5.2.2 Retransmission of MARS_JOIN and MARS_LEAVE messages.
5.2.3 Registering with the MARS. Cluster member registration and deregistration.
5.3 Support for Layer 3 group management.
5.4 Support for redundant/backup MARS entities.
5.4.1 First response to MARS problems.
5.4.2 Connecting to a backup MARS.
5.4.3 Dynamic backup lists, and soft redirects.
5.5 Data path LLC/SNAP encapsulations for transmit and receive. encapsulations.
6. The MARS in greater detail.
6.1 Class I MARS requirements. Basic interface to Cluster members.
6.1.1 Response to MARS_REQUEST.
6.1.2 Response to MARS_JOIN and MARS_LEAVE.
6.1.3 Generating MARS_REDIRECT_MAP.
6.1.4 Cluster Sequence Numbers.
6.2 Class II MARS requirements.
6.2.1 Class II MARS response interface to a MARS_REQUEST. Multicast Servers (MCSs).
6.2.1 MARS_REQUESTs for MCS supported groups.
6.2.2 MARS_MSERV and MARS_UNSERV messages.
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6.2.3 Registering a Multicast Server (MCS).
6.2.4 Class II Modified response to MARS_JOIN and MARS_LEAVE.
6.2.5 Sequence numbers for ServerControlVC traffic.
6.3 Why global sequence numbers?
6.4 Redundant/Backup MARS Architectures.
7. How an MCS utilises a Class II MARS.
7.1 Association with a particular Layer 3 group.
7.2 Termination of incoming VCs.
7.3 Management of outgoing VC.
7.4 Use of a backup MARS.
8. Support for IP multicast routers.
8.1 Forwarding into a Cluster.
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8.2 Joining in 'promiscuous' mode.
8.3 Forwarding across the cluster.
8.4 Joining in 'semi-promiscous' mode.
8.5 An alternative to IGMP Queries.
8.6 CMIs across multiple interfaces.
9. Multiprotocol applications of the MARS and MARS clients.
10. Supplementary parameter processing.
10.1 Interpreting the ar$extoff field.
10.2 The format of TLVs.
10.3 Processing MARS messages with TLVs.
10.4 Initial set of TLV elements.
11. Key Decisions and open issues.
Acknowledgments
References
Appendix A. Hole punching algorithms for Class II MARS messages. algorithms.
Appendix B. Minimising the impact of IGMP in IPv4 environments.
Appendix C. Further comments on 'Clusters'.
Appendix D. TLV list parsing algorithm.
Appendix E. Summary of timer values.
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1. Introduction.
Multicasting is the process whereby a source host or protocol entity
sends a packet to multiple destinations simultaneously using a
single, local 'transmit' operation. The more familiar cases of
Unicasting and Broadcasting may be considered to be special cases of
Multicasting (with the packet delivered to one destination, or 'all'
destinations, respectively).
Most network layer models, like the one described in RFC 1112 [1] for
IP multicasting, assume sources may send their packets to an abstract
'multicast group addresses'. Link layer support for such an
abstraction is assumed to exist, and is provided by technologies such
as Ethernet.
ATM is being utilized as a new link layer technology to support a
variety of protocols, including IP. With RFC 1483 [2] the IETF
defined a multiprotocol mechanism for encapsulating and transmitting
packets using AAL5 over ATM Virtual Channels (VCs). However, the ATM
Forum's currently published signalling specification (UNI 3.0 [4],
with additions for UNI 3.1 released in late 1994) [4])
does not provide the multicast address abstraction. Unicast
connections are supported by point to point, bidirectional VCs.
Multicasting is supported through point to multipoint unidirectional
VCs. The key limitation is that the sender must have prior knowledge
of each intended recipient, and explicitly establish a VC with itself
as the root node and the recipients as the leaf nodes.
This document has two broad goals:
Define a group address registration and membership distribution
mechanism that allows UNI 3.1 based networks to support the
multicast service of protocols such as IP.
Define specific endpoint behaviour behaviours for managing point to
multipoint VCs to achieve efficient multicasting of layer 3 packets.
As the IETF is currently in the forefront of using wide area
multicasting this document's descriptions will often focus on IP
service model of RFC 1112. A final chapter will note the
multiprotocol application of the architecture.
This document avoids discussion of one highly non-trivial aspect of
using ATM - the specification of QoS for VCs being established in
response to higher layer needs. Research in this area is still very
formative,
formative [7], and so it is assumed that future documents will further
clarify the mapping of QoS requirements to VC establishment. The
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default at this time is that VCs SHOULD be are established with a request for
Unspecified Bit Rate (UBR) service (as service, as typified by the IETF's use of
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VCs for unicast IP, described in RFC 1755 [6]). [6].
1.1 The Multicast Address Resolution Server (MARS).
The Multicast Address Resolution Server (MARS) is a superset of the
ATM ARP Server introduced in RFC 1577 [3]. It acts as a registry,
associating layer 3 multicast group identifiers with the ATM
interfaces representing the group's members. MARS messages, based on
the ATM ARP format, support the distribution of multicast group
membership information between MARS and endpoints (hosts or routers).
Endpoint address resolution entities query the MARS when a layer 3
address needs to be resolved to the set of ATM endpoints making up
the group at any one time. Endpoints keep the MARS informed when they
need to join or leave particular layer 3 groups. To provide for
asynchronous notification of group membership changes the MARS
manages a point to multipoint VC out to all endpoints desiring
multicast support
Valid arguments can be made for two different approaches to ATM level
multicasting of layer 3 packets - through meshes of point to
multipoint VCs, or ATM level multicast servers (MCS). Two classes of The MARS are described - Class I (allowing VC meshes to support layer 3
traffic), and Class II (which
architecture allows either VC meshes or MCSs to be
assigned for use used on a per-group basis). per-
group basis.
1.2 The ATM level multicast Cluster.
Each MARS manages a 'cluster' of ATM-attached endpoints. A Cluster is
defined as
The set of ATM interfaces chosen to participate in direct ATM
connections to achieve multicasting of AAL_SDUs between
themselves.
In practice, a Cluster is the set of endpoints that choose to use the
same MARS to register their memberships and receive their updates
from.
By implication of this definition, traffic between interfaces
belonging to different Clusters passes through an inter-cluster
device. (In the IP world an inter-cluster device would be an IP
multicast router with logical interfaces into each Cluster.) This
document explicitly avoids specifying the nature of inter-cluster
(layer 3) routing protocols.
The mapping of clusters to other constrained sets of endpoints (such
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as unicast Logical IP Subnets) is left to each network administrator.
A simple approach in overlaid IP environments would be
However, for the purposes of conformance with this document network
administrators MUST ensure that each LIS
to be Logical IP Subnet (LIS) is
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served by a separate MARS, with the creating a one-to-one mapping between
cluster being built from
the LIS members. and unicast LIS. IP multicast routers would then interconnect each
LIS as they do with conventional subnets. However, there is no requirement
that a cluster be limited to a single LIS. (Relaxation of this
restriction MAY only occur after future research on the interaction
between existing layer 3 multicast routing protocols and unicast
subnet boundaries.)
1.3 Document overview.
This document assumes an understanding of concepts explained in
greater detail in RFC 1112, RFC 1577, UNI 3.1, and RFC 1755 [6].
Section 2 provides an overview of IP multicast and what RFC 1112
required from Ethernet.
Section 3 describes in more detail the multicast support services
offered by UNI 3.1, and outlines the differences between VC meshes
and multicast servers (MCSs) as mechanisms for distributing packets
to multiple destinations.
Section 4 provides an overview of the MARS and its relationship to
ATM endpoints. This section also discusses the encapsulation and
structure of MARS control messages, and some encapsulation issues for data traffic. messages.
Section 5 substantially defines the entire cluster member endpoint
behaviour, on both receive and transmit sides. This includes both
normal operation and error recovery.
Section 6 summarises the requirements required behaviour of a Class I MARS, and provides
a detailed description of the Class II MARS.
Section 7 looks at how a multicast server (MCS) interacts with a
Class II
MARS.
Section 8 discusses how IP multicast routers may make novel use of
promiscuous and semi-promiscuous group joins. Also discussed is a
mechanism designed to reduce the amount of IGMP traffic issued by
routers.
Section 9 discusses how this document applies in the more general
(non-IP) case.
Section 10 summarises the key proposals, and identifies areas for
future research that are generated by this MARS architecture.
The appendices provide discussion on issues that arise out the
implementation of this memo. document. Appendix A discusses MARS and
endpoint algorithms for parsing MARS messages. Appendix B describes
the
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possible interim work-arounds. Finally, Appendix C discusses the use
of 'clusters' 'cluster'
concept in further detail.
2. Summary of the IP multicast service model.
Under IP detail, while Appendix D briefly outlines an
algorithm for parsing TLV lists.
1.4 Conventions.
In this document the following coding and packet representation rules
are used:
All multi-octet parameters are encoded in big-endian form (i.e.
the most significant octet comes first).
In all multi-bit parameters bit numbering begins at 0 for the
least significant bit when stored in memory (i.e. the n'th bit has
weight of 2^n).
A bit that is 'set', 'on', or 'one' holds the value 1.
A bit that is 'reset', 'off', 'clear', or 'zero' holds the value
0.
2. Summary of the IP multicast service model.
Under IP version 4 (IPv4), addresses in the range of 224.0.0.0 and
239.255.255.255 are termed 'Class D' or 'multicast group' addresses.
These abstractly represent all the IP hosts in the Internet (or some
constrained subset of the Internet) who have decided to 'join' the
specified group.
RFC1112 requires that a multicast-capable IP interface must support
the transmission of IP packets to an IP multicast group address,
whether or not the node considers itself a 'member' of that group.
Consequently, group membership is effectively irrelevant to the
transmit side of the link layer interfaces. When Ethernet is used as
the link layer (the example used in RFC1112), no address resolution
is required to transmit packets. An algorithmic mapping from IP
multicast address to Ethernet multicast address is performed locally
before the packet is sent out the local interface in the same 'send
and forget' manner as a unicast IP packet.
Joining and Leaving an IP multicast group is more explicit on the
receive side - with the primitives JoinLocalGroup and LeaveLocalGroup
affecting what groups the local link layer interface should accept
packets from. When the IP layer wants to receive packets from a
group, it issues JoinLocalGroup. When it no longer wants to receive
packets, it issues LeaveLocalGroup. A key point to note is that
changing state is a local issue, it has no affect on other hosts
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attached to the Ethernet.
IGMP is defined in RFC 1112 to support IP multicast routers attached
to a given subnet. Hosts issue IGMP Report messages when they perform
a JoinLocalGroup, or in response to an IP multicast router sending an
IGMP Query. By periodically transmitting queries IP multicast routers
are able to identify what IP multicast groups have non-zero
membership on a given subnet.
A specific IP multicast address, 224.0.0.1, is allocated for the
transmission of IGMP Query messages. All IP multicast hosts must
issue JoinLocalGroup for 224.0.0.1 during their initialisation. Each
host keeps a list of IP multicast groups it has been JoinLocalGroup'd
to. When a router issues an IGMP Query on 224.0.0.1 each host begins
to send IGMP Reports for each group it is a member of. IGMP Reports
are sent to the group address, not 224.0.0.1, "so that other members
of the same group on the same network can overhear the Report" and
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not bother sending one of their own. IP multicast routers conclude
that a group has no members on the subnet when IGMP Queries no longer
elict associated replies.
3. UNI 3.1 support for intra-cluster multicasting.
This document will describe its operation in terms of 'generic'
functions that should be available to clients of a UNI 3.1 signalling
entity in a given ATM endpoint. The ATM model broadly describes an
'AAL User' as any entity that establishes and manages VCs and
underlying AAL services to exchange data. An IP over ATM interface is
a form of 'AAL User' (although the default LLC/SNAP encapsulation
mode specified in RFC1755 really requires that an 'LLC entity' is the
AAL User, which in turn supports the IP/ATM interface).
The most fundamental limitations of UNI 3.1's multicast support are:
Only point to multipoint, unidirectional VCs may be established.
Only the root (source) node of a given VC may add or remove leaf
nodes.
Leaf nodes are identified by their unicast ATM addresses. UNI 3.1
defines two ATM address formats - native E.164 and NSAP (although it
must be stressed that the NSAP address is so called because it uses
the NSAP format - an ATM endpoint is NOT a Network layer termination
point). In UNI 3.1 an 'ATM Number' is the primary identification of
an ATM endpoint, and it may use either format. Under some
circumstances an ATM endpoint must be identified by both a native
E.164 address (identifying the attachment point of a private network
to a public network), and an NSAP address ('ATM Subaddress')
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identifying the final endpoint within the private network. For the
rest of this document the term will be used to mean either a single
'ATM Number' or an 'ATM Number' combined with an 'ATM Subaddress'.
3.1 VC meshes.
The most fundamental approach to intra-cluster multicasting is the
multicast VC mesh. Each source establishes its own independent point
to multipoint VC (a single multicast tree) to the set of leaf nodes
(destinations) that it has been told are members of the group it
wishes to send packets to.
Interfaces that are both senders and group members (leaf nodes) to a
given group will originate one point to multipoint VC, and terminate
one VC for every other active sender to the group. This criss-
crossing of VCs across the ATM network gives rise to the name 'VC
mesh'.
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3.2 Multicast Servers.
An alternative model has each source establish a VC to an
intermediate node - the multicast server (MCS). The multicast server
itself establishes and manages a point to multipoint VC out to the
actual desired destinations.
The MCS reassembles AAL_SDUs arriving on all the incoming VCs, and
then queues them for transmission on its single outgoing point to
multipoint VC. (Reassembly of incoming AAL_SDUs is required at the
multicast server as AAL5 does not support cell level multiplexing of
different AAL_SDUs on a single outgoing VC.)
The leaf nodes of the multicast server's point to multipoint VC must
be established prior to packet transmission, and the multicast server
requires an external mechanism to identify them. A side-effect of
this method is that ATM interfaces that are both sources and group
members will receive copies of their own packets back from the MCS
(An alternative method is for the multicast server to explicitly
retransmit packets on individual VCs between itself and group
members. A benefit of this second approach is that the multicast
server can ensure that sources do not receive copies of their own
packets.)
An
The simplest MCS does NOT pay any pays no attention to the contents of each AAL_SDU.
It is purely an AAL/ATM level device. More complex MCS architectures
(where a single endpoint serves multiple layer 3 groups) are
possible, but are beyond the scope of this document. More detailed
discussion is provided in section 7.
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3.3 Tradeoffs.
Arguments over the relative merits of VC meshes and multicast servers
have raged for some time. Ultimately the choice depends on the
relative trade-offs a system administrator must make between
throughput, latency, congestion, and resource consumption. Even
criteria such as latency can mean different things to different
people - is it end to end packet time, or the time it takes for a
group to settle after a membership change? The final choice depends
on the characteristics of the applications generating the multicast
traffic.
If we focussed on the data path we might prefer the VC mesh because
it lacks the obvious single congestion point of an MCS. Throughput
is likely to be higher, and end to end latency lower, because the
mesh lacks the intermediate AAL_SDU reassembly that must occur in
MCSs. The underlying ATM signalling system also has greater
opportunity to ensure optimal branching points at ATM switches along
the multicast trees originating on each source.
However, resource consumption will be higher. Every group member's
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ATM interface must terminate a VC per sender (consuming on-board
memory for state information, instance of an AAL service, and
buffering in accordance with the vendors particular architecture). On
the contrary, with a multicast server only 2 VCs (one out, one in)
are required, independent of the number of senders. The allocation of
VC related resources is also lower within the ATM cloud when using a
multicast server. These points may be considered to have merit in
environments where VCs across the UNI or within the ATM cloud are
valuable (e.g. the ATM provider charges on a per VC basis), or AAL
contexts are limited in the ATM interfaces of endpoints (many current
implementations allow only 2k, 1k, or less). endpoints.
If we focus on the signalling load then MCSs have the advantage when
faced with dynamic sets of receivers. Every time the membership of a
multicast group changes (a leaf node needs to be added or dropped),
only a single point to multipoint VC needs to be modified when using
an MCS. This generates a single signalling event across the MCS's
UNI. However, when membership change occurs in a VC mesh, signalling
events occur at the UNIs of every traffic source - the transient
signalling load scales with the number of sources. This has obvious
ramifications if you define latency as the time for a group's
connectivity to stabilise after change (especially as the number of
senders increases).
Finally, as noted above, MCSs introduce a 'reflected packet' problem,
which requires additional per-AAL_SDU information to be carried in
order for layer 3 sources to detect their own AAL_SDUs coming back.
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The Class II MARS architecture allows system administrators to utilize either
approach on a group by group basis.
3.4 Interaction with local UNI 3.1 signalling entity.
The following generic signalling functions are presumed to be
available to local AAL Users:
L_CALL_RQ - Establish a unicast VC to a specific endpoint.
L_MULTI_RQ - Establish multicast VC to a specific endpoint.
L_MULTI_ADD - Add new leaf node to previously established VC.
L_MULTI_DROP - Remove specific leaf node from established VC.
L_RELEASE - Release unicast VC, or all Leaves of a multicast VC.
The signalling exchanges and local information passed between AAL
User and UNI 3.1 signalling entity with these functions are outside
the scope of this document.
The following indications are assumed to be available to AAL Users,
generated by by the local UNI 3.1 signalling entity:
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L_ACK - Succesful completion of a local request.
L_REMOTE_CALL - A new VC has been established to the AAL User.
ERR_L_RQFAILED - A remote ATM endpoint rejected an L_CALL_RQ,
L_MULTI_RQ, or L_MULTI_ADD.
ERR_L_RELEASE
ERR_L_DROP - A remote ATM endpoint terminated dropped off an existing VC.
ERR_L_RELEASE - An existing VC was terminated.
The signalling exchanges and local information passed between AAL
User and UNI 3.1 signalling entity with these functions are outside
the scope of this document.
4. Overview of the MARS.
The MARS may reside within any ATM endpoint that is directly
addressable by the endpoints it is serving. Endpoints wishing to join
a multicast cluster must be configured with the ATM address of the
node on which the cluster's MARS resides. (Section 5.4 describes how
backup MARSs may be added to support the activities of a cluster.
References to 'the MARS' in following sections will be assumed to
mean the acting MARS for the cluster.)
4.1 Architecture.
Architecturally the MARS is an evolution of the RFC 1577 ARP Server.
Whilst the ARP Server keeps a table of {IP,ATM} address pairs for all
IP endpoints in an LIS, the MARS keeps extended tables of {layer 3
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address, ATM.1, ATM.2, ..... ATM.n} mappings. It can either be
configured with certain mappings, or dynamically 'learn' mappings.
The format of the {layer 3 address} field is generally not
interpreted by the MARS (except for a few special cases, described
later).
A single MARS may not support more than one cluster (by definition).
However, a single ATM node may support multiple logical MARSs, each of which
support a separate cluster. The restriction is that each MARS has a
unique ATM address (e.g. a different SEL field in the NSAP address of
the node on which the multiple MARSs reside)
Two classes reside). By definition a single
instance of a MARS are defined in this memo - Class I (with the
minimum may not support required to enable multicasting using VC meshes), and
Class II (Class I + extensions to support the introduction of MCSs).
Both Class I and Class II MARS distributes group membership
information more than one cluster.
The MARS distributes group membership update information to cluster
members over a point to multipoint VC known as the ClusterControlVC. A Class II MARS
Additionally, when Multicast Servers (MCSs) are being used it also
establishes a separate point to multipoint VC out to registered MCSs,
known as the ServerControlVC. All cluster members are leaf nodes of
ClusterControlVC. All registered multicast servers are leaf nodes of
ServerControlVC (described further in section 6).
The MARS does NOT take part in the actual multicasting of layer 3
data packets.
4.2 Control message format.
The MARS message format is an extension of the ATM ARP message
format. By default all MARS messages MUST be LLC/SNAP encapsulated
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in accordance with RFC 1483, using the same encapsulation manner as ATM ARP: ATMARP messages:
[0xAA-AA-03][0x00-00-00][0x08-06][MARS message]
(LLC) (OUI) (PID)
The
MARS messages may further be subdivided.
[MARS header][Layer 3 and/or ATM addresses][Supplementary TLVs]
[MARS header] contains fields indicating the operation being
performed and the layer 3 protocol being referred to (e.g IPv4, IPv6,
AppleTalk, etc). (The choice of common encapsulation and message header
format means that MARS and ARP Server functionality may be
implemented within a common
entity if entity, and share a network designer client-server VC, if
the implementor so chooses.
Finally, chooses.)
The format of the following [Layer 3 and/or ATM addresses] area in
the MARS does NOT take part message depends on the operation indicated in the actual multicasting [MARS
header]. These provide the fundamental information that the
registrations, queries, and updates use and operate on.
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A list of
layer 3 data packets.
5. Endpoint (MARS client) interface behaviour. TLV (type, length, value) encoded information elements may
be appended to provide supplementary information. This section describes feature is
described in further detail the operation of what might best in section 10.
MARS messages contain variable length address fields. In all cases
null addresses MUST be
thought of encoded as a 'shim layer', sitting between your layer 3 protocol's
link layer interface zero length, and the underlying UNI 3.1 service. An endpoint have no space
allocated in this context can be a host or a router - any entity that requires
a generic 'layer 3 over ATM' interface to support layer 3 multicast.
It is broken into two key subsections - one for the transmit side,
and one for message.
4.3 Common header values in MARS messages.
The [MARS header] specifically consists of the receive side.
Multiple logical following fields:
Data:
ar$hrd 16 bits Hardware type ( 19 decimal, 0x13 hex)
ar$pro 16 bits Protocol type
ar$shtl 8 bits Type & length of source ATM interfaces may be supported by a single physical number
ar$sstl 8 bits Type & length of source ATM interface (for example, using different SEL values in subaddress
ar$op 16 bits Operation code.
ar$extoff 32 bits Extensions Offset.
[...rest of MARS message....]
In all cases the NSAP
formatted address assigned ar$hrd field is set to the physical 0x13, to indicate ATM interface). Therefore
implementors MUST allow for multiple independent 'layer 3 over ATM'
interfaces too, each with its own configured MARS (or table of MARSs, as discussed the
underlying hardware type.
The ar$op field identifies whether the message is a MARS, ARP, or
Inverse ARP message. The values used by this document are summarised
in section 5.4), 11.
The ar$pro field identifies the higher layer protocol whose addresses
are being carried and ability to be attached or mapped to hardware addresses identified by
the same
or different clusters.
The primary signalling paths between ar$hrd field. If the ar$op field indicates a MARS client (managing an
endpoint) and their associated MARS is message, the
ar$pro value represents a transient point protocol from the following two sets:
0x0000 to point,
bidirectional VC. This VC is established 0x05FF Reserved for future use by the MARS client, IETF.
0x0600 to 0xFFFF Protocols defined by the equivalent Ethertypes.
The use of the ar$pro field is described further in section 9.
The ar$extoff field identifies the existence and location of
supplementary parameters. Its use is described in section 10.
The remaining fields are used in manners specific to send queries to, and receive replies from, the MARS. It has
an operation
being performed, and are described in later sections.
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5. Endpoint (MARS client) interface behaviour.
An endpoint is best thought of as a 'shim' or 'convergence' layer,
sitting between a layer 3 protocol's link layer interface and the
underlying UNI 3.1 service. An endpoint in this context can exist in
a host or a router - any entity that requires a generic 'layer 3 over
ATM' interface to support layer 3 multicast. It is broken into two
key subsections - one for the transmit side, and one for the receive
side.
Multiple logical ATM interfaces may be supported by a single physical
ATM interface (for example, using different SEL values in the NSAP
formatted address assigned to the physical ATM interface). Therefore
implementors MUST allow for multiple independent 'layer 3 over ATM'
interfaces too, each with its own configured MARS (or table of MARSs,
as discussed in section 5.4), and ability to be attached to the same
or different clusters.
The initial signalling path between a MARS client (managing an
endpoint) and its associated MARS is a transient point to point,
bidirectional VC. This VC is established by the MARS client, and is
used to send queries to, and receive replies from, the MARS. It has
an associated idle timer, and is dismantled if not used for a
configurable period of time. The minimum suggested value for this
time is 1 minute, and the RECOMMENDED default is 20 minutes. Where (Where
the MARS and ARP Server are co-resident, this VC may be used for both
ATM ARP traffic and MARS traffic. control traffic.)
The remaining signalling path is ClusterControlVC, to which the MARS
client is added as a leaf node when it registers (described in
section 5.2.3).
Most of this specification is concerned with managing and
distributing information that allows the establishment of VCs for
actually carrying layer 3 data packets. The actual format of the data
carried on these VCs is almost completely outside the scope of this
specification. However, when using MCSs (described in section 3)
endpoints need to filter out the reflected packets that can occur.
The solution to this problem in a general way requires the use of
additional per-packet encapsulation. This is discussed in section 5.5
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MARS messages contain variable length address fields. In all cases
null addresses MUST be encoded as zero length, and have no space
allocated in the message. Addresses with non-zero length, but zero
value can have specific meanings to the MARS, and MUST NOT be used in
any other fashion.
5.1 Transmit side behaviour.
The following description will often be in terms of an IP/ATM IPv4/ATM
interface that is capable of transmitting packets to a Class D
address at any time, without prior warning. It should be trivial for
an implementor to generalise this behaviour to the requirements of
another layer 3 data protocol.
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When a packet arrives for transmission, and there is no outgoing VC
already marked as serving the packet's multicast destination address,
the MARS is queried for the set of ATM endpoints currently making up
the multicast group.
The query is executed by issuing a MARS_REQUEST. The MARS_REQUEST
message is formatted as an ATM ARP_REQUEST (RFC 1577) with operation
type code (ar$op field) of 11 (decimal). The reply from the
MARS may take one of two forms:
MARS_MULTI - Sequence of MARS_MULTI messages returning the set of
ATM endpoints that are to be leaf nodes of the
outgoing VC.
MARS_NAK - No mapping found, group is empty.
The formats of these messages are described in section 5.1.2.
Outgoing VCs are established with a request for Unspecified Bit Rate
(UBR) service, as typified by the IETF's use of VCs for unicast IP,
described in RFC 1755 [6]. Future documents may vary this approach
and allow the specification of different ATM traffic parameters from
locally configured information or parameters obtained through some
external means.
5.1.1 Retrieving Group Membership from the MARS.
If the MARS had no mapping for the desired Class D address a MARS_NAK
will be returned. In this case the IP packet MUST be discarded
silently. If a match is found in the MARS's tables it proceeds to
return addresses ATM.1 through ATM.n in a sequence of one or more
MARS_MULTIs. A simple mechanism is used to detect and recover from
loss of MARS_MULTI messages.
Each MARS_MULTI carries a boolean field x, and a 15 bit integer field
y - expressed as MARS_MULTI(x,y). Field y acts as a sequence number,
starting at 1 and incrementing for each MARS_MULTI sent. Field x
acts as an 'end of reply' marker. When x == 1 the MARS response is
considered complete.
In addition, each MARS_MULTI may carry multiple ATM addresses from
the set {ATM.1, ATM.2, .... ATM.n}. A MARS MUST minimise the number
of MARS_MULTIs transmitted by placing as many group member's
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addresses in a single MARS_MULTI as possible. The limit on the length
of an individual MARS_MULTI message MUST be the MTU of the underlying
VC.
Assume
For example, assume n ATM addresses must be returned, each MARS_MULTI
is limited to only p ATM addresses, and p << n. This would require a
sequence of k MARS_MULTI messages (where k = (n/p)+1, using integer
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arithmetic), transmitted as follows:
MARS_MULTI(0,1) carries back {ATM.1 ... ATM.p}
MARS_MULTI(0,2) carries back {ATM.(p+1) ... ATM.(2p)}
[.......]
MARS_MULTI(1,k) carries back { ... ATM.n}
If k == 1 then only MARS_MULTI(1,1) is sent.
Typical failure mode will be losing one or more of MARS_MULTI(0,1)
through MARS_MULTI(0,k-1). This is detected when y jumps by more than
one between consecutive MARS_MULTI's. An alternative failure mode is
losing MARS_MULTI(1,k). A timer MUST be implemented to flag the
failure of the last MARS_MULTI to arrive. A default value of 10
seconds is suggested. RECOMMENDED.
If a 'sequence jump' is detected, the host MUST wait for the
MARS_MULTI(1,k), discard all results, and repeat the MARS_REQUEST.
If a timeout occurs, the host MUST discard all results, and repeat
the MARS_REQUEST.
(Corruption of cell contents will lead to loss of a MARS_MULTI
through AAL5 CPCS_PDU reassembly failure, which will be detected
through the mechanisms described above.)
If the MARS is managing a cluster of endpoints spread across
different but directly accessible ATM networks it will not be able to
return all the group members in a single MARS_MULTI. The MARS_MULTI
message format allows for either E.164, ISO NSAP, or (E.164 + NSAP)
to be returned as ATM addresses. However, each MARS_MULTI message may
only return ATM addresses of the same type and length. The returned
addresses MUST be grouped according to type (E.164, ISO NSAP, or
both) and returned in a sequence of separate MARS_MULTI parts.
5.1.2 MARS_REQUEST, MARS_MULTI, and MARS_NAK messages.
MARS_REQUEST is an RFC1577 ATM ARP_REQUEST, but with shown below. It is indicated an 'operation type
value' (ar$op) of 11 (decimal). 11.
The multicast address being resolved is placed into the the target
protocol address field (ar$tpa). The (ar$tpa), and the target hardware address is
set to null (ar$thtl and ar$tstl both
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In IPv4 environments the protocol type (ar$pro) is 2048 (decimal). Section 6.6 of RFC
1577 should 0x800 and the
target protocol address length (ar$tpln) MUST be consulted for specific details set to 4. The source
fields MUST contain the ATM number and coding subaddress of the
ar$shtl and ar$sstl fields.
MARS_NAK is client
issuing the MARS_REQUEST returned with operation (the subaddress MAY be null).
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Data:
ar$hrd 16 bits Hardware type value of 16
(decimal). All other fields should be left unchanged from the
MARS_REQUEST.
The MARS_MULTI message is identified by an 'operation type value' of
12 (decimal). The message format is:
Data:
ar$hrd 16 bits Hardware type ( 19 decimal, 0x13 hex)
ar$pro ( 19 decimal, 0x13 hex)
ar$pro 16 bits Protocol type
ar$shtl 8 bits Type & length of source ATM number (q)
ar$sstl 8 bits Type & length of source ATM subaddress (r)
ar$op 16 bits Operation code (MARS_MULTI) (MARS_REQUEST)
ar$extoff 32 bits Extensions Offset.
ar$spln 8 bits Length of source protocol address (s)
ar$thtl 8 bits Type & length of target ATM number (x)
ar$tstl 8 bits Type & length of target ATM subaddress (y)
ar$tpln 8 bits Length of target multicast group address (z)
ar$tnum 16 bits Number of target ATM addresses returned (N).
ar$seqxy 16 bits Boolean flag x and sequence number y.
ar$msn 32 bits MARS Sequence Number.
ar$sha qoctets source ATM number
ar$ssa roctets source ATM subaddress
ar$spa soctets source protocol address
ar$tpa zoctets target multicast group address
ar$tha.1 xoctets target ATM number 1
ar$tsa.1 yoctets target ATM subaddress 1
ar$tha.2
ar$tha xoctets target ATM number 2
ar$tsa.2
ar$tsa yoctets target ATM subaddress 2
[.......]
ar$tha.N xoctets target ATM number N
ar$tsa.N yoctets
ar$tpa zoctets target ATM subaddress N
ar$seqxy is coded with flag x in multicast group address
Following the leading bit, RFC1577 approach, the ar$shtl, ar$sstl, ar$thtl and sequence number
y
ar$tstl fields are coded as an unsigned integer in the remaining 15 bits.
0 1
0 1 2 3 4 5 6 follows:
7 8 9 0 1 2 3 4 5 6
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|x| y 5 4 3 2 1 0
+-+-+-+-+-+-+-+-+
|0|x| length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
ar$tnum
+-+-+-+-+-+-+-+-+
The most significant bit is reserved and MUST be set to zero. The
second most significant bit (x) is a flag indicating whether the ATM
address being referred to is in:
- ATM Forum NSAPA format (x = 0).
- Native E.164 format (x = 1).
The bottom 6 bits is an unsigned integer value indicating how many pairs the length
of
{ar$tha,ar$tsa} (i.e. how many group member's the associated ATM addresses) are
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present address in the message. ar$msn is an octets.
The ar$spln and ar$tpln fields are unsigned 32 8 bit number filled integers, giving
the length in
by octets of the source and target protocol address fields
respectively.
MARS before transmitting each MARS_MULTI. Its packets use is described
further in section 5.1.4. Section 6.6 of RFC 1577 should be consulted
for specific details and coding of all other true variable length fields.
As an example, assume we have a multicast cluster using 4 byte
protocol addresses, 20 byte ATM numbers, A null (non-existant)
address MUST be coded as zero length, and 0 byte ATM subaddresses.
For n group members in a single MARS_MULTI we require a (44 + 20n)
byte message. If we assume the default MTU of 9180 bytes, we can
return a maximum of 456 group member's addresses no space allocated for it
in a single
MARS_MULTI.
5.1.3 Establishing the outgoing multipoint VC.
Following message body.
MARS_NAK is the completion MARS_REQUEST returned with operation type value of 16
(decimal). All other fields are left unchanged from the MARS_MULTI reply MARS_REQUEST
(e.g. do not transpose the endpoint may
establish a new point source and target information. In all
cases MARS clients use the source address fields to multipoint VC, or reuse an existing one.
If establishing a new VC, an L_MULTI_RQ identify their
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own messages coming back).
The MARS_MULTI message is issued for ATM.1, followed identified by an L_MULTI_ADD for every member ar$op value of the set {ATM.2, ....ATM.n}
(assuming the set is non-null). 12. The packet is then transmitted over
the newly created VC just as it would be for a unicast VC.
After transmitting the packet, the local interface holds the VC open
and marks it as the active path out of the host for any subsequent IP
packets being sent to that Class D address.
When establishing a new
message format is:
Data:
ar$hrd 16 bits Hardware type ( 19 decimal, 0x13 hex)
ar$pro 16 bits Protocol type
ar$shtl 8 bits Type & length of source ATM number (q)
ar$sstl 8 bits Type & length of source ATM subaddress (r)
ar$op 16 bits Operation code (MARS_MULTI)
ar$extoff 32 bits Extensions Offset.
ar$spln 8 bits Length of source protocol address (s)
ar$thtl 8 bits Type & length of target ATM number (x)
ar$tstl 8 bits Type & length of target ATM subaddress (y)
ar$tpln 8 bits Length of target multicast VC it is possible that one or more
L_MULTI_RQ or L_MULTI_ADD may fail. The UNI 3.1 failure cause must
be group address (z)
ar$tnum 16 bits Number of target ATM addresses returned in the ERR_L_RQFAILED signal (N).
ar$seqxy 16 bits Boolean flag x and sequence number y.
ar$msn 32 bits MARS Sequence Number.
ar$sha qoctets source ATM number
ar$ssa roctets source ATM subaddress
ar$spa soctets source protocol address
ar$tpa zoctets target multicast group address
ar$tha.1 xoctets target ATM number 1
ar$tsa.1 yoctets target ATM subaddress 1
ar$tha.2 xoctets target ATM number 2
ar$tsa.2 yoctets target ATM subaddress 2
[.......]
ar$tha.N xoctets target ATM number N
ar$tsa.N yoctets target ATM subaddress N
The source protocol and ATM address fields are copied directly from
the local signalling
entity to the AAL User. If the failure cause MARS_REQUEST that this MARS_MULTI is not 49 (Quality of
Service unavailable) or 51 (user cell rate not available), in response to (not the
endpoint's ATM address MARS
itself).
ar$seqxy is dropped from coded with flag x in the set {ATM.1, ATM.2, ...,
ATM.n} returned by the MARS. Otherwise, the L_MULTI_RQ or
L_MULTI_ADD should be reissued after a delay of 10 to 20 seconds. If
the request fails again, another request should be issued after twice
the previous delay has elapsed. This process should be continued
until the call succeeds or the multipoint VC gets released.
If the initial L_MULTI_RQ fails for ATM.1, leading bit, and n is greater than 1
(i.e. sequence number
y coded as an unsigned integer in the returned set remaining 15 bits.
| 1st octet | 2nd octet |
7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|x| y |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
ar$tnum is an unsigned integer indicating how many pairs of
{ar$tha,ar$tsa} (i.e. how many group member's ATM addresses contains 2 or more addresses)
a new L_MULTI_RQ should be immediately issued for the next ATM
address are
present in the set. This procedure is repeated until an L_MULTI_RQ
succeeds, as no L_MULTI_ADDs may be issued until an initial outgoing
VC message. ar$msn is established.
Each ATM address for which an L_MULTI_RQ failed with cause 49 or 51
MUST be tagged rather than deleted. An L_MULTI_ADD is issued for
these tagged addresses using unsigned 32 bit number filled in
by the random delay procedure outlined MARS before transmitting each MARS_MULTI. Its use is described
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above.
The VC MAY be considered 'up' before failed L_MULTI_ADDs
further in section 5.1.4.
As an example, assume we have been
successfully re-issued. An endpoint MAY implement a concurrent
mechanism that allows data to start flowing out the new VC even while
failed L_MULTI_ADDs are being re-tried. (The alternative of waiting
for each leaf node to accept multicast cluster using 4 byte
protocol addresses, 20 byte ATM numbers, and 0 byte ATM subaddresses.
For n group members in a single MARS_MULTI we require a (48 + 20n)
byte message. If we assume the connection could lead to significant
delays default MTU of 9180 bytes, we can
return a maximum of 456 group member's addresses in transmitting a single
MARS_MULTI.
5.1.3 Establishing the first packet.)
Each VC MUST have outgoing multipoint VC.
Following the completion of the MARS_MULTI reply the endpoint may
establish a configurable inactivity timer associated with it. new point to multipoint VC, or reuse an existing one.
If the timer expires, establishing a new VC, an L_RELEASE L_MULTI_RQ is issued for that VC, and the
Class D address is no longer considered to have ATM.1, followed
by an active path out L_MULTI_ADD for every member of the local host. The timer SHOULD be no less than 1 minute, and a
default of 20 minutes set {ATM.2, ....ATM.n}
(assuming the set is RECOMMENDED. Choice of specific timer
periods non-null). The packet is beyond then transmitted over
the scope of this document. newly created VC consumption may also just as it would be reduced by endpoints noting when a new
group's set of {ATM.1, ....ATM.n} matches that of for a pre-existing VC
out to another group. With careful unicast VC.
After transmitting the packet, the local management, interface holds the VC open
and assuming marks it as the
QoS active path out of the existing VC is sufficient host for both groups, a new pt any subsequent IP
packets being sent to mpt
VC may not be necessary. Under certain circumstances endpoints may
decide that Class D address.
When establishing a new multicast VC it is sufficient possible that one or more
L_MULTI_RQ or L_MULTI_ADD may fail. The UNI 3.1 failure cause must
be returned in the ERR_L_RQFAILED signal from the local signalling
entity to re-use an existing VC whose set the AAL User. If the failure cause is not 49 (Quality of
leaf nodes
Service unavailable) or 51 (user cell rate not available), the
endpoint's ATM address is dropped from the set {ATM.1, ATM.2, ...,
ATM.n} returned by the MARS. Otherwise, the L_MULTI_RQ or
L_MULTI_ADD should be reissued after a superset random delay of 5 to 10
seconds. If the new group's membership (in which case
some endpoints will receive multicast traffic request fails again, another request should be
issued after twice the previous delay has elapsed. This process
should be continued until the call succeeds or the multipoint VC gets
released.
If the initial L_MULTI_RQ fails for a layer 3 group
they haven't joined, ATM.1, and must filter them above n is greater than 1
(i.e. the ATM interface).
Algorithms for performing this type returned set of optimization are not discussed
here, and are not required for conformance with this memo.
5.1.4 Monitoring updates on ClusterControlVC.
Once ATM addresses contains 2 or more addresses)
a new VC has been established, L_MULTI_RQ should be immediately issued for the transmit side of next ATM
address in the cluster
member's interface needs to monitor subsequent group changes - adding
or dropping leaf nodes as appropriate. set. This procedure is achieved by watching
for MARS_JOIN and MARS_LEAVE messages from the MARS itself. These
messages are described in detail in section 5.2 - at this point it repeated until an L_MULTI_RQ
succeeds, as no L_MULTI_ADDs may be issued until an initial outgoing
VC is
sufficient to note that they carry:
- The established.
Each ATM address of a node joining or leaving a group.
- The layer 3 address of the group(s) being joined or left.
- A Cluster Sequence Number (CSN) from the MARS.
MARS_JOIN and MARS_LEAVE messages arrive at each cluster member
across ClusterControlVC. MARS_JOIN for which an L_MULTI_RQ failed with cause 49 or MARS_LEAVE messages that simply
confirm information already held by the cluster member are used to
track 51
MUST be tagged rather than deleted. An L_MULTI_ADD is issued for
these tagged addresses using the Cluster Sequence Number, but are otherwise ignored. random delay procedure outlined
above.
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5.1.4.1 Updating the active VCs.
If
The VC MAY be considered 'up' before failed L_MULTI_ADDs have been
successfully re-issued. An endpoint MAY implement a MARS_JOIN is seen concurrent
mechanism that refers allows data to (or encompasses) a group start flowing out the new VC even while
failed L_MULTI_ADDs are being re-tried. (The alternative of waiting
for
which each leaf node to accept the transmit side already has a connection could lead to significant
delays in transmitting the first packet.)
Each VC open, MUST have a configurable inactivity timer associated with it.
If the new member's ATM
address is extracted and timer expires, an L_MULTI_ADD L_RELEASE is issued locally. This ensures for that endpoints already sending to a given group will immediately add VC, and the new member to their list of recipients.
If a MARS_LEAVE
Class D address is seen that refers no longer considered to (or encompasses) a group for
which the transmit side already has a VC open, have an active path out of
the old member's ATM
address is extracted local host. The timer SHOULD be no less than 1 minute, and an L_MULTI_DROP issued locally. This ensures
that endpoints already sending to a given group will immediately drop
the old member from their list
default of recipients. When the last leaf 20 minutes is RECOMMENDED. Choice of a
VC specific timer
periods is dropped, beyond the scope of this document.
VC is closed completely and the affected group no
longer have consumption may also be reduced by endpoints noting when a path out new
group's set of the local endpoint (the next outbound
packet to {ATM.1, ....ATM.n} matches that group's address will trigger the creation of a new VC,
as described in sections 5.1.1 pre-existing VC
out to 5.1.3).
In an IPv4 environment any endpoint leaving 224.0.0.1 another group. With careful local management, and assuming the
QoS of the existing VC is assumed to
be ceasing support sufficient for IP multicast operation. If both groups, a MARS_LEAVE is
seen that refers new pt to group 224.0.0.1 then the ATM address of the
endpoint specified in the message MUST be removed from every
multipoint mpt
VC on which may not be necessary. Under certain circumstances endpoints may
decide that it is listed as a leaf node.
The transmit side of the interface MUST NOT shut down sufficient to re-use an active existing VC to whose set of
leaf nodes is a group for which superset of the new group's membership (in which case
some endpoints will receive side has just executed multicast traffic for a
LeaveLocalGroup. This behaviour is consistent with layer 3 group
they haven't joined, and must filter them above the model of
hosts transmitting to groups regardless ATM interface).
Algorithms for performing this type of their own membership
status.
If a MARS_JOIN or MARS_LEAVE arrives with ar$pnum == 0 it carries no
<min,max> pairs, optimization are not discussed
here, and is only used for tracking the CSN (and possibly are not required for confirming conformance with this document.
5.1.4 Tracking subsequent group updates.
Once a new VC has been established, the transmission transmit side of the local cluster
member's own
MARS_JOIN interface needs to monitor subsequent group changes - adding
or MARS_LEAVE, dropping leaf nodes as described in section 5.2.2).
5.1.4.2 Tracking the Cluster Sequence Number.
It appropriate. This is important that endpoints do not miss group membership updates
issued achieved by watching
for MARS_JOIN and MARS_LEAVE messages from the MARS over ClusterControlVC. However, itself. These
messages are described in detail in section 5.2 - at this will happen
from time point it is
sufficient to time. note that they carry:
- The ATM address of a node joining or leaving a group.
- The layer 3 address of the group(s) being joined or left.
- A Cluster Sequence Number is carried as an
unsigned 32 bit value in (CSN) from the ar$msn field of many MARS messages
(except for MARS_REQUEST MARS.
MARS_JOIN and MARS_NAK). It increments once for every
transmission MARS_LEAVE messages arrive at each cluster member
across ClusterControlVC. MARS_JOIN or MARS_LEAVE messages that simply
confirm information already held by the MARS makes on ClusterControlVC, regardless of
whether cluster member are used to
track the transmission represents a change in Cluster Sequence Number, but are otherwise ignored.
5.1.4.1 Updating the MARS database or
not. By tracking this counter, cluster members can determine whether
they have missed a previous message on ClusterControlVC, and possibly active VCs.
If a membership change. This MARS_JOIN is then used seen that refers to trigger revalidation
(described in section 5.1.5). (or encompasses) a group for
which the transmit side already has a VC open, the new member's ATM
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The current CSN
address is copied into the ar$msn field of MARS messages
being sent to cluster members, whether out ClusterControlVC or on extracted and an
point to point VC.
Calculations on the sequence numbers MUST be performed as unsigned 32
bit arithmetic, L_MULTI_ADD issued locally. This ensures
that endpoints already sending to ensure no glitches when a given group will immediately add
the counters roll over.
Every cluster new member keeps its own 32 bit Host Sequence Number (HSN) to track the MARS's sequence number. Whenever their list of recipients.
If a message MARS_LEAVE is received seen that carries an ar$msn field the following processing is performed:
Seq.diff = ar$msn - HSN
ar$msn -> HSN
{...process MARS message as appropriate...}
if ((Seq.diff != 1) && (Seq.diff != 0))
then {...revalidate refers to (or encompasses) a group membership information...}
The basic result for
which the transmit side already has a VC open, the old member's ATM
address is extracted and an L_MULTI_DROP issued locally. This ensures
that endpoints already sending to a given group will immediately drop
the cluster old member attempts to keep locked
in step with membership changes noted by the MARS. If it ever detects
that a membership change occurred (in any group) without it noticing,
it re-validates the membership of all groups it currently has
multicast VCs open to.
The ar$msn value in an individual MARS_MULTI is not used to update
the HSN until all parts from their list of recipients. When the MARS_MULTI (if more than 1) have
arrived. However, the ar$msn field in consecutive messages last leaf of a
multi-part MARS_MULTI MUST be constant. If the ar$msn field changes
before
VC is dropped, the MARS_MULTI VC is closed completely received, then the entire
MARS_MULTI MUST be discarded at and the completion affected group no
longer has a path out of the response, and
the MARS_REQUEST re-issued.
The MARS is free local endpoint (the next outbound packet
to choose an initial value that group's address will trigger the creation of CSN. When a new
cluster member starts up it should initialise HSN VC, as
described in sections 5.1.1 to zero. When the
cluster member sends the MARS_JOIN 5.1.3).
In an IPv4 environment any endpoint leaving 224.0.0.1 is assumed to register (described later), the
HSN will
be correctly updated ceasing support for IP multicast operation. If a MARS_LEAVE is
seen that refers to group 224.0.0.1 then the current CSN value when ATM address of the
endpoint receives specified in the copy of its MARS_JOIN back message MUST be removed from the MARS.
5.1.5 Revalidating every
multipoint VC on which it is listed as a VC's leaf nodes.
Certain events may inform a cluster member that it has incorrect
information about the sets node.
The transmit side of leaf nodes it should be sending to. If the interface MUST NOT shut down an error occurs on a active VC associated with to
a particular group, the
cluster member initiates revalidation procedures group for that specific
group. If which the receive side has just executed a jump
LeaveLocalGroup. (This behaviour is detected in consistent with the Cluster Sequence Number, this
initiates revalidation model of all groups to which the cluster member
currently has open point
hosts transmitting to multipoint VCs.
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Each open and active multipoint VC has groups regardless of their own membership
status.)
If a flag associated MARS_JOIN or MARS_LEAVE arrives with ar$pnum == 0 it
called 'VC_revalidate'. This flag is checked everytime a packet carries no
<min,max> pairs, and is
queued only used for tracking the CSN (and possibly
for confirming the transmission on that VC. If of the flag is false, local cluster member's own
MARS_JOIN or MARS_LEAVE, as described in section 5.2.2).
5.1.4.2 Tracking the packet
is transmitted and no further action Cluster Sequence Number.
It is required.
However, if important that endpoints do not miss group membership updates
issued by the VC_revalidate flag MARS over ClusterControlVC. However, this will happen
from time to time. The Cluster Sequence Number is true then carried as an
unsigned 32 bit value in the packet is
transmitted and a new sequence ar$msn field of events is started locally.
Revalidation begins with re-issuing a many MARS messages
(except for MARS_REQUEST and MARS_NAK). It increments once for every
transmission the group
being revalidated. The returned set of members {NewATM.1, NewATM.2,
.... NewATM.n} is compared with the set already held locally.
L_MULTI_DROPs are issued MARS makes on ClusterControlVC, regardless of
whether the group's VC for each node that appears transmission represents a change in the original set of MARS database or
not. By tracking this counter, cluster members but not in the revalidated set of
members. L_MULTI_ADDs are issued can determine whether
they have missed a previous message on the group's VC for each node that
appears in the revalidated set of members but not ClusterControlVC, and possibly
a membership change. This is then used to trigger revalidation
(described in the original set
of members. section 5.1.5).
The VC_revalidate flag current CSN is reset when revalidation
concludes for copied into the given group. Implementation specific mechanisms
will ar$msn field of MARS messages
being sent to cluster members, whether out ClusterControlVC or on an
point to point VC.
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Calculations on the sequence numbers MUST be needed performed as unsigned 32
bit arithmetic.
Every cluster member keeps its own 32 bit Host Sequence Number (HSN)
to flag track the 'revalidation in progress' state.
The key difference between constructing a VC (section 5.1.3) and
revalidating MARS's sequence number. Whenever a VC message is received
that packet transmission continues on carries an ar$msn field the open
VC while it following processing is being revalidated. This minimises the disruption to
existing traffic.
The general algorithm for initiating revalidation is: performed:
Seq.diff = ar$msn - When a packet arrives for transmission on a given group,
the groups HSN
ar$msn -> HSN
{...process MARS message as appropriate...}
if ((Seq.diff != 1) && (Seq.diff != 0))
then {...revalidate group membership information...}
The basic result is revalidated if VC_revalidate == TRUE.
Revalidation resets VC_revalidate.
- When an event occurs that demands revalidation, every
group has its VC_revalidate flag set TRUE at the cluster member attempts to keep locked
in step with membership changes noted by the MARS. If it ever detects
that a random time
between 1 and 10 seconds.
Benefit: Revalidation membership change occurred (in any group) without it noticing,
it re-validates the membership of active groups occurs quickly, and
essentially idle all groups are revalidated as needed. Randomly
distributed setting of VC_revalidate flag improves chances of
staggered revalidation requests from senders when a sequence number
jump it currently has
multicast VCs open to.
The ar$msn value in an individual MARS_MULTI is detected.
5.1.5.1 When leaf node drops itself.
During not used to update
the life HSN until all parts of the MARS_MULTI (if more than 1) have
arrived. However, the ar$msn field in consecutive messages of a multipoint VC an ERR_L_RELEASE may
multi-part MARS_MULTI MUST be received
indicating that a leaf node has terminated its participation at constant. If the
ATM level. The ATM endpoint associated with ar$msn field changes
before the ERR_L_RELEASE MARS_MULTI is completely received, then the entire
MARS_MULTI MUST be
removed from the locally held set {ATM.1, ATM.2, .... ATM.n}
associated with discarded at the VC.
After a random period completion of time between 1 the response, and 10 seconds
the
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VC_revalidate flag associated with that VC MUST be set true.
5.1.5.2 When a jump MARS_REQUEST re-issued.
The MARS is detected in the free to choose an initial value of CSN.
Section 5.1.4.2 describes how a CSN jump is detected. If a CSN jump
is detected upon receipt of When a new
cluster member starts up it should initialise HSN to zero. When the
cluster member sends the MARS_JOIN or a MARS_LEAVE then every
outgoing multicast VC MUST have its VC_revalidate flag set true at
some random interval between 1 and 10 seconds from when to register (described later), the CSN jump
was detected.
The only exception
HSN will be correctly updated to this rule is if a sequence number jump is
detected during the establishment current CSN value when the
endpoint receives the copy of its MARS_JOIN back from the MARS.
5.1.5 Revalidating a new group's VC (i.e. VC's leaf nodes.
Certain events may inform a
MARS_MULTI reply was correctly received, but its ar$msn indicated cluster member that some previous MARS traffic had been missed on ClusterControlVC).
In this case every open VC, EXCEPT the one just established, MUST
have its VC_revalidate flag set true at some random interval between
1 and 10 seconds from when it has incorrect
information about the CSN jump was detected. (The sets of leaf nodes it should be sending to. If
an error occurs on a VC being
established at associated with a particular group, the time is considered already validated.)
5.2. Receive side behaviour.
A
cluster member is a 'group member' (in the sense initiates revalidation procedures for that it receives
packets directed at specific
group. If a given multicast group) when its ATM address
appears jump is detected in the MARS's table entry for Cluster Sequence Number, this
initiates revalidation of all groups to which the group's cluster member
currently has open point to multipoint VCs.
Each open and active multipoint VC has a flag associated with it
called 'VC_revalidate'. This flag is checked everytime a packet is
queued for transmission on that VC. If the flag is false, the packet
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is transmitted and no further action is required.
However, if the VC_revalidate flag is true then the packet is
transmitted and a new sequence of events is started locally.
Revalidation begins with re-issuing a MARS_REQUEST for the group
being revalidated. The returned set of members {NewATM.1, NewATM.2,
.... NewATM.n} is compared with the set already held locally.
L_MULTI_DROPs are issued on the group's VC for each node that appears
in the original set of members but not in the revalidated set of
members. L_MULTI_ADDs are issued on the group's VC for each node that
appears in the revalidated set of members but not in the original set
of members. The VC_revalidate flag is reset when revalidation
concludes for the given group. Implementation specific mechanisms
will be needed to flag the 'revalidation in progress' state.
The key difference between constructing a VC (section 5.1.3) and
revalidating a VC is that packet transmission continues on the open
VC while it is being revalidated. This minimises the disruption to
existing traffic.
The algorithm for initiating revalidation is:
- When a packet arrives for transmission on a given group,
the groups membership is revalidated if VC_revalidate == TRUE.
Revalidation resets VC_revalidate.
- When an event occurs that demands revalidation, every
group has its VC_revalidate flag set TRUE at a random time
between 1 and 10 seconds.
Benefit: Revalidation of active groups occurs quickly, and
essentially idle groups are revalidated as needed. Randomly
distributed setting of VC_revalidate flag improves chances of
staggered revalidation requests from senders when a sequence number
jump is detected.
5.1.5.1 When leaf node drops itself.
During the life of a multipoint VC an ERR_L_DROP may be received
indicating that a leaf node has terminated its participation at the
ATM level. The ATM endpoint associated with the ERR_L_DROP MUST be
removed from the locally held set {ATM.1, ATM.2, .... ATM.n}
associated with the VC.
After a random period of time between 1 and 10 seconds the
VC_revalidate flag associated with that VC MUST be set true.
If an ERR_L_RELEASE is received then the entire set {ATM.1, ATM.2,
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.... ATM.n} is cleared and the VC is considered to be completely shut
down. Further packet transmission to the group served by this VC will
result in a new VC being established as described in section 5.1.3.
5.1.5.2 When a jump is detected in the CSN.
Section 5.1.4.2 describes how a CSN jump is detected. If a CSN jump
is detected upon receipt of a MARS_JOIN or a MARS_LEAVE then every
outgoing multicast VC MUST have its VC_revalidate flag set true at
some random interval between 1 and 10 seconds from when the CSN jump
was detected.
The only exception to this rule is if a sequence number jump is
detected during the establishment of a new group's VC (i.e. a
MARS_MULTI reply was correctly received, but its ar$msn indicated
that some previous MARS traffic had been missed on ClusterControlVC).
In this case every open VC, EXCEPT the one just established, MUST
have its VC_revalidate flag set true at some random interval between
1 and 10 seconds from when the CSN jump was detected. (The VC being
established at the time is considered already validated.)
5.2. Receive side behaviour.
A cluster member is a 'group member' (in the sense that it receives
packets directed at a given multicast group) when its ATM address
appears in the MARS's table entry for the group's multicast address.
A key function within each cluster is the distribution of group
membership information from the MARS to cluster members.
An endpoint may wish to 'join a group' in response to a local, higher
level request for membership of a group, or because the endpoint
supports a layer 3 multicast forwarding engine that requires the
ability to 'see' intra-cluster traffic in order to forward it.
Two messages support these requirements - MARS_JOIN and MARS_LEAVE.
These are sent to the MARS by endpoints when the local layer 3/ATM
interface is requested to join or leave a multicast group. The MARS
propagates these messages back out over ClusterControlVC, to ensure
the knowledge of the group's membership change is distributed in a
timely fashion to other cluster members.
Certain models of layer 3 endpoints (e.g. IP multicast routers)
expect to be able to receive packet traffic 'promiscuously' across
all groups. This functionality may be emulated by allowing routers
to request that the MARS returns them as 'wild card' members of all
Class D addresses. However, a problem inherent in the current ATM
model is that a completely promiscuous router may exhaust the local
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reassembly resources in its ATM interface. MARS_JOIN supports a
generalisation to the notion of 'wild card' entries, enabling routers
to limit themselves to 'blocks' of the Class D address space. Use of
this facility is described in greater detail in Section 8.
A block can be as small as 1 (a single group) or as large as the
entire multicast address space (e.g. default IPv4 'promiscuous'
behaviour). A block is defined as all addresses between, and
inclusive of, a <min,max> address pair. A MARS_JOIN or MARS_LEAVE may
carry multiple <min,max> pairs.
Cluster members MUST provide ONLY a single <min,max> pair in each
JOIN/LEAVE message they issue. However, they MUST be able to process
multiple <min,max> pairs in JOIN/LEAVE messages when performing VC
management as described in section 5.1.4 (the interpretation being
that the join/leave operation applies to all addresses in range from
<min> to <max> inclusive, for every <min,max> pair).
In RFC1112 environments a MARS_JOIN for a single group is triggered
by a JoinLocalGroup signal from the IP layer. A MARS_LEAVE for a
single group is triggered by a LeaveLocalGroup signal from the IP
layer.
Cluster members with special requirements (e.g. multicast routers)
may issue MARS_JOINs and MARS_LEAVEs specifying a block of multicast
group addresses.
An endpoint MUST register with a MARS in order to become a member of
a cluster and be added as a leaf to ClusterControlVC. Registration
is covered in section 5.2.3.
Finally, the endpoint MUST be capable of terminating unidirectional
VCs (i.e. act as a leaf node of a UNI 3.1 point to multipoint VC,
with zero bandwidth assigned on the return path). RFC 1755 describes
the signalling information required to terminate VCs carrying
LLC/SNAP encapsulated traffic (discussed further in section 5.5).
5.2.1 Format of the MARS_JOIN and MARS_LEAVE Messages.
The MARS_JOIN message is indicated by an operation type value of 14
(decimal). MARS_LEAVE has the same format and operation type value of
15 (decimal). The message format is:
Data:
ar$hrd 16 bits Hardware type (0x13)
ar$pro 16 bits Protocol type
ar$shtl 8 bits Type & length of source ATM number (q)
ar$sstl 8 bits Type & length of source ATM subaddress (r)
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ar$op 16 bits Operation code (MARS_JOIN or MARS_LEAVE)
ar$extoff 32 bits Extensions Offset.
ar$spln 8 bits Length of source protocol address (s)
ar$tpln 8 bits Length of multicast group address (z)
ar$pnum 16 bits Number of multicast group address pairs (N)
ar$flags 16 bits layer3grp, copy, and register flags.
ar$cmi 16 bits Cluster Member ID
ar$msn 32 bits MARS Sequence Number.
ar$sha qoctets source ATM number (E.164 or ATM Forum NSAPA).
ar$ssa roctets source ATM subaddress (ATM Forum NSAPA).
ar$spa soctets source protocol address
ar$min.1 zoctets Minimum multicast group address - pair.1
ar$max.1 zoctets Maximum multicast group address - pair.1
[.......]
ar$min.N zoctets Minimum multicast group address - pair.N
ar$max.N zoctets Maximum multicast address.
A key function within each cluster is group address - pair.N
ar$spln indicates the distribution number of group
membership information from bytes in the MARS to cluster members.
An endpoint may wish to 'join a group' source endpoint's
protocol address, and is interpreted in response to a local, higher
level request for membership the context of a group, or because the endpoint
supports a layer 3 multicast forwarding engine that requires protocol
indicated by the
ability to 'see' intra-cluster traffic ar$pro field. (e.g. in order to forward it.
Two messages support these requirements - MARS_JOIN IPv4 environments ar$pro will
be 0x800, ar$spln is 4, and MARS_LEAVE.
These are sent to the MARS by endpoints when the local layer 3/ATM
interface ar$tpln is requested to join or leave a multicast group. 4.)
The MARS
propagates these messages back out over ClusterControlVC, to ensure
the knowledge of the group's membership change is distributed in a
timely fashion to other cluster members.
Certain models of layer 3 endpoints (e.g. IP multicast routers)
expect to ar$flags field contains three flags:
Bit 15 - ar$flags.layer3grp.
Bit 14 - ar$flags.copy.
Bit 13 - ar$flags.register.
The lower 13 unused bits MUST be able to receive packet traffic 'promiscuously' across
all groups. This functionality may zero.
ar$flags.copy MUST be emulated by allowing routers set to request that the MARS returns them as 'wild card' members of all
Class D addresses. However, a problem inherent in 0 when the current ATM
model message is that a completely promiscuous router may exhaust the local
reassembly resources in its ATM interface. MARS_JOIN supports being sent from a
generalisation
MARS client, and MUST be set to 1 when the notion of 'wild card' entries, enabling routers
to limit themselves message is being sent from
a MARS. (This flag is intended to 'blocks' support integrating the MARS
function with one of the Class D address space. Use MARS clients in your cluster. The
destination of
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this facility is an incoming MARS_JOIN can be determined from its
value.)
ar$flags.layer3grp allows the MARS to provide the group membership
information described further in greater detail in Section 8.
A block can section 5.3. The rules for its use
are:
ar$flags.layer3grp MUST be as small as 1 (a single group) or as large as set when the
entire cluster member is issuing
the MARS_JOIN a the result of a layer 3 multicast address space group being
explicitly joined. (e.g. default IPv4 'promiscuous'
behaviour). A block is defined as all addresses between, and
inclusive of, a <min,max> address pair. A MARS_JOIN or MARS_LEAVE may
carry multiple <min,max> pairs.
Cluster members MUST provide ONLY result of a single <min,max> pair JoinHostGroup operation
in each
JOIN/LEAVE message they issue. However, they an RFC1112 compliant host).
ar$flags.layer3grp MUST be able to process
multiple <min,max> pairs in JOIN/LEAVE messages when performing VC
management as described reset in section 5.1.4 (the interpretation being
that each MARS_JOIN if the join/leave operation applies to all addresses in range from
<min> to <max> inclusive, for every <min,max> pair).
In RFC1112 environments a
MARS_JOIN for a single is simply the local ip/atm interface registering to
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receive traffic on that group for its own reasons.
ar$flags.layer3grp is triggered
by a JoinLocalGroup signal from ignored and MUST be treated as reset by the IP layer. A MARS_LEAVE
MARS for any MARS_JOIN that specifies a block covering more than a
single group is triggered by a LeaveLocalGroup signal from the IP
layer.
Cluster members with special requirements (e.g. multicast routers)
may issue MARS_JOINs and MARS_LEAVEs specifying a block of multicast
group addresses.
An endpoint MUST join from a router ensuring their
forwarding engines 'see' all traffic).
ar$flags.register indicates whether the MARS_JOIN or MARS_LEAVE is
being used to register with or deregister a MARS cluster member (described in order
section 5.2.3). When used to become join or leave specific groups the
ar$register flag MUST be zero.
ar$pnum indicates how many <min,max> pairs are included in the
message. This field MUST be 1 when the message is sent from a member of cluster
member. A MARS MAY return a MARS_JOIN or MARS_LEAVE with any ar$pnum
value, including zero. This will be explained futher in section
6.2.4.
The ar$cmi field MUST be zeroed by cluster members, and be added as a leaf to ClusterControlVC. Registration is covered used by
the MARS during cluster member registration, described in section
5.2.3.
Finally, the endpoint
ar$msn MUST be capable of terminating unidirectional
VCs (i.e. act as a leaf node of a UNI 3.1 point zero when transmitted by an endpoint. It is set to multipoint VC).
RFC 1755 describes the information required to terminate VCs carrying
LLC/SNAP encapsulated traffic (discussed further
current value of the Cluster Sequence Number by the MARS when the
MARS_JOIN or MARS_LEAVE is retransmitted. Its use has been described
in section 5.5).
5.2.1 Format 5.1.4.
To simplify construction and parsing of MARS_JOIN and MARS_LEAVE
messages, the following restrictions are imposed on the <min,max>
pairs:
Assume max(N) is the <max> field from the MARS_JOIN and MARS_LEAVE Messages.
The MARS_JOIN message Nth <min,max> pair.
Assume min(N) is indicated by an operation type value of 14
(decimal). MARS_LEAVE has the same format and operation type value of
15 (decimal). The <min> field from the Nth <min,max> pair.
Assume a join/leave message format is:
Data:
ar$hrd 16 bits Hardware type (19 decimal)
ar$pro 16 bits Protocol type
ar$shtl 8 bits Type & length of source ATM number (q)
ar$sstl 8 bits Type & length of source ATM subaddress (r)
ar$op 16 bits Operation code (MARS_JOIN or MARS_LEAVE)
ar$spln 8 bits Length of source protocol address (s)
ar$tpln 8 bits Length arrives with K <min,max> pairs.
The following must hold:
max(N) < min(N+1) for 1 <= N < K
max(N) >= min(N) for 1 <= N <= K
In plain language, the set must specify an ascending sequence of multicast group
address (z)
ar$pnum 16 bits Number blocks. The definition of multicast group address pairs (N)
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ar$resv 16 bits ar$layer3grp flag, and 15 bits reserved.
ar$cmi 16 bits Cluster Member ID
ar$msn 32 bits MARS Sequence Number.
ar$sha qoctets source ATM number (E.164 "greater" or ATM Forum NSAPA).
ar$ssa roctets source ATM subaddress (ATM Forum NSAPA).
ar$spa soctets source "less than" may be
protocol address
ar$min.1 zoctets Minimum multicast group address - pair.1
ar$max.1 zoctets Maximum multicast group address - pair.1
[.......]
ar$min.N zoctets Minimum multicast group address - pair.N
ar$max.N zoctets Maximum multicast specific. In IPv4 environments the addresses are treated as
32 bit, unsigned binary values (most significant byte first).
5.2.1.1 Important IPv4 default values.
The JoinLocalGroup and LeaveLocalGroup operations are only valid for
a single group. For any arbitrary group address - pair.N
Refer X the associated
MARS_JOIN or MARS_LEAVE MUST specify a single pair <X, X>.
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ar$flags.layer3grp MUST be set under these circumstances.
A router choosing to RFC 1577, section 6.6 for behave strictly in accordance with RFC1112 MUST
specify the coding entire Class D space. The associated MARS_JOIN or
MARS_LEAVE MUST specify a single pair <224.0.0.0, 239.255.255.255>.
Whenever a router issues a MARS_JOIN only in order to forward IP
traffic it MUST reset ar$flags.layer3grp.
The use of the ar$shtl alternative <min, max> values by multicast routers is
discussed in Section 8.
5.2.2 Retransmission of MARS_JOIN and
ar$sstl fields. ar$spln indicates MARS_LEAVE messages.
Transient problems may result in the number loss of bytes in messages between the source
endpoint's protocol address,
MARS and cluster members
A simple algorithm is interpreted in used to solve this problem. Cluster members
retransmit each MARS_JOIN and MARS_LEAVE message at regular intervals
until they receive a copy back again, either on ClusterControlVC or
the context of VC on which they are sending the
protocol indicated by message. At this point the ar$pro field. (e.g. in IPv4 environments
ar$pro will
local endpoint can be 0x800, ar$spln is 4, certain that the MARS received and ar$tpln is 4.) processed
it.
The ar$resv field contains a flag - ar$layer3grp - in its most
significant bit, interval should be no shorter than 5 seconds, and 15 unused bits which a default value
of 10 seconds is recommended. After 5 retransmissions the attempt
should be flagged locally as a failure. This MUST be zero. This flag is
to allow the considered as a
MARS to provide failure, and triggers the 'short cut' group membership
information MARS reconnection described further in section 5.3. The rules for its use
are:
ar$layer3grp MUST be set when the cluster member
5.4.
A 'copy' is issuing the
MARS_JOIN a the result of a layer 3 multicast group being
explicitly joined. (e.g. defined as seeing a result message of a JoinHostGroup the same operation code
(and ar$flags.register value) containing the local host's identity in an RFC1112 compliant host).
the source address fields. The flag MUST <min,max> pair set is not checked,
and does not have to be reset in each MARS_JOIN if the MARS_JOIN same (this is
simply the local ip/atm interface registering required to receive traffic
on that group for its own reasons.
The flag is ignored and MUST be treated as reset by compatible
with the MARS for
any MARS_JOIN modification that specifies a block covering more than a single
group (e.g. a block join from a router ensuring their forwarding
engines 'see' all traffic).
ar$pnum indicates how many <min,max> pairs are included in MARS may effect on the
message. retransmitted
MARS_JOIN or MARS_LEAVE message).
This field must always be 1 when the algorithm explicitly allows only ONE outstanding MARS_JOIN and
MARS_LEAVE message is sent from a
cluster member. (It will be unchanged when returned by at a Class I
MARS. A Class II MARS time (although you may return have one of both
outstanding).
5.2.3 Cluster member registration and deregistration.
To become a MARS_JOIN or MARS_LEAVE cluster member an endpoint must register with any
ar$pnum value, including zero. the MARS.
This will be explained futher in
section 6.2.4.)
The ar$cmi field SHOULD be zeroed by cluster members, achieves two things - the endpoint is added as a leaf node of
ClusterControlVC, and the endpoint is used by assigned a 16 bit Cluster
Member Identifier (CMI). The CMI uniquely identifies each endpoint
that is attached to the MARS during cluster member registration, described in section
5.2.3. cluster.
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ar$msn MUST be zero
Registration with the MARS occurs when transmitted by an endpoint. It is endpoint issues a MARS_JOIN
with the ar$flags.register flag set to the
current value one (bit 13 of the Cluster Sequence Number by the MARS ar$flags
field).
The cluster member MUST include its source ATM address, and MAY
choose to specify a null source protocol address when the registering.
No protocol specific group addresses are included in a registration
MARS_JOIN.
The cluster member retransmits this MARS_JOIN or MARS_LEAVE is retransmitted. Its use has been described in accordance with
section 5.1.4.
To simplify construction and parsing of MARS_JOIN and MARS_LEAVE
messages, the following restrictions are imposed on the <min,max>
pairs:
Assume max(N) is 5.2.2 until it confirms that the <max> field from MARS has received it.
When the Nth <min,max> pair.
Assume min(N) registration MARS_JOIN is returned it contains a non-zero
value in ar$cmi. This value MUST be noted by the <min> field from cluster member, and
used whenever circumstances require the Nth <min,max> pair.
Assume cluster member's CMI.
An endpoint may also choose to de-register, using a join/leave message arrives MARS_LEAVE with K <min,max> pairs.
The following must hold:
max(N) < min(N+1) for 1 <= N < K
max(N) >= min(N) for 1 <= N <= K
In plain english,
ar$flags.register set. This would result in the MARS dropping the
endpoint from ClusterControlVC, removing all references to the set must specify an ascending sequence of
address blocks. The definition of "greater" or "less than" may be
protocol specific. In IPv4 environments member
in the addresses are treated as
32 bit, unsigned binary values (most significant byte first).
5.2.1.1 Important IPv4 default values.
The JoinLocalGroup mapping database, and LeaveLocalGroup operations are only valid freeing up its CMI.
As for registration, a single group. For any arbitrary group deregistration request MUST include the
correct source ATM address X for the associated
MARS_JOIN or MARS_LEAVE MUST cluster member, but MAY choose to
specify a single pair <X, X>. In general
the ar$layer3grp flag MUST be set under these circumstances.
A router choosing to behave strictly null source protocol address.
The cluster member retransmits this MARS_LEAVE in accordance with RFC1112 MUST
specify
section 5.2.2 until it confirms that the entire Class D space. The associated MARS_JOIN or
MARS_LEAVE MUST specify a single pair <224.0.0.0, 239.255.255.255>.
Whenever a router issues a MARS_JOIN only in order MARS has received it.
5.3 Support for Layer 3 group management.
Whilst the intention of this specification is to forward IP
traffic it MUST reset be independent of
layer 3 issues, an attempt is being made to assist the ar$layer3grp flag.
The use operation of alternative <min, max> values by
layer 3 multicast routers routing protocols that need to ascertain if any
groups have members within a cluster.
One example is
discussed IP, where IGMP is used (as described in Section 8.
5.2.2 Retransmission of MARS_JOIN and MARS_LEAVE messages.
Transient problems section 2)
simply to determine whether any other cluster members are listening
to a group because they have higher layer applications that want to
receive a group's traffic.
Routers may result in the loss of messages between choose to query the MARS and cluster members
A simple algorithm is used to solve for this problem. Cluster members
retransmit each MARS_JOIN information, rather
than multicasting IGMP queries to 224.0.0.1 and MARS_LEAVE message at regular intervals
until they receive a copy back again, either on ClusterControlVC or incurring the
associated cost of setting up a VC on which they are sending the message. At this point to all systems in the
local endpoint can be certain that cluster.
The query is issued by sending a MARS_GROUPLIST_REQUEST to the MARS received and processed
it. MARS.
MARS_GROUPLIST_REQUEST is built from a MARS_JOIN, but it has an
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The interval should be no shorter than 5 seconds, and a default value
operation code of 10 seconds is recommended. After 5 retransmissions the attempt
should be flagged locally as a failure. This 20 (ar$op = 20). A single <min,max> pair MUST be considered as a
MARS failure,
provided (ar$pnum = 1), and triggers it specifies the MARS reconnection described in section
5.4.
A 'copy' is defined as seeing a message range of the same operation code
containing the local host's identity groups in which
the source address fields.
The <min,max> pair set querying cluster member is not checked, and does not have to be interested.
The response from the
same (this MARS is required to be compatible with the modification that a
Class II MARS may effect on the retransmitted MARS_JOIN or MARS_LEAVE
message).
This algorithm explicitly allows only ONE outstanding MARS_JOIN and
MARS_LEAVE message at MARS_GROUPLIST_REPLY, carrying a time (although you may list
of the multicast groups within the specified <min,max> block that
have Layer 3 members. A group is noted in this list if one or more
of both
outstanding).
5.2.3 Registering with the MARS.
To become MARS_JOINs that generated its mapping entry in the MARS
contained a set ar$flags.layer3grp flag.
MARS_GROUPLIST_REPLYs are transmitted back to the querying cluster
member an endpoint must register with on the MARS.
This achieves two things - VC used to send the endpoint MARS_GROUPLIST_REQUEST.
MARS_GROUPLIST_REPLY is added as a leaf node of
ClusterControlVC, and derived from the endpoint MARS_MULTI, it may have
multiple parts if needed, and is assigned received in a similar manner.
Data:
ar$hrd 16 bit Cluster
Member Identifier (CMI). The CMI uniquely identifies each endpoint
that is attached to the cluster.
Registration with the MARS occurs when an endpoint issues a MARS_JOIN
for a bits Hardware type ( 19 decimal, 0x13 hex)
ar$pro 16 bits Protocol type
ar$shtl 8 bits Type & length of source ATM number (q)
ar$sstl 8 bits Type & length of source ATM subaddress (r)
ar$op 16 bits Operation code (MARS_GROUPLIST_REPLY)
ar$extoff 32 bits Extensions Offset.
ar$spln 8 bits Length of source protocol specific address (s)
ar$thtl 8 bits Unused - set to zero.
ar$tstl 8 bits Unused - set to zero.
ar$tpln 8 bits Length of target multicast group address.
In IPv4 environments an endpoint (whether in a host address (z)
ar$tnum 16 bits Number of group addresses returned (N).
ar$seqxy 16 bits Boolean flag x and sequence number y.
ar$msn 32 bits MARS Sequence Number.
ar$sha qoctets source ATM number (E.164 or router) MUST
explicitly issue a MARS_JOIN for the special ATM Forum NSAPA).
ar$ssa roctets source ATM subaddress (ATM Forum NSAPA).
ar$spa soctets source protocol address "0.0.0.0" in
order to register with the MARS. In other words, a MARS_JOIN with
ar$tpln of 4, and 8 bytes of zero starting at ar$min.1 (equivalent to
the block of <0.0.0.0,0.0.0.0>. This function may be internal to
ar$mgrp.1 zoctets Group address 1
[.......]
ar$mgrp.N zoctets Group address N
ar$seqxy is coded as for the
IP/ATM driver, MARS_MULTI - multiple
MARS_GROUPLIST_REPLY components are transmitted and does not require the IP layer to believe it has
'joined' received using
the all-zeroes IP address.
The specific addresses signifying 'registration' for other layer 3
protocols will be defined in subsequent documents.
The cluster member retransmits this MARS_JOIN same algorithm as described in accordance with section 5.2.2 until it confirms that the MARS has received it.
When the registration MARS_JOIN 5.1.1 for MARS_MULTI. The
only difference is that protocol address are being returned it contains a non-zero
value rather
than ATM addresses.
As for MARS_MULTIs, if an error occurs in ar$cmi. This value the reception of a multi
part MARS_GROUPLIST_REPLY the whole thing MUST be noted by the cluster member, discarded and
used whenever circumstances require the cluster member's CMI.
An endpoint may also choose to de-register, using a MARS_LEAVE. In an
IPv4 environment a MARS_LEAVE on
MARS_GROUPLIST_REQUEST re-issued. (This includes the special address of "0.0.0.0" ar$msn value
being constant.)
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would result in the MARS dropping
Note that the endpoint from ClusterControlVC ability to generate MARS_GROUPLIST_REQUEST messages,
and freeing up its CMI
5.3 Support for Layer 3 group management.
Whilst the intention of this specification receive MARS_GROUPLIST_REPLY messages, is to be independent of
layer 3 issues, an attempt not required for
general host interface implementations. It is optional for interfaces
being made implemented to assist the operation of support layer 3 multicast routing protocols that need to ascertain if any
groups have members within a cluster.
One example is IP, where IGMP is used (as described in section 2)
simply to determine whether any other cluster members forwarding engines.
However, this functionality MUST be supported by the MARS.
5.4 Support for redundant/backup MARS entities.
Endpoints are listening assumed to a group because they have higher layer applications that want to
receive a group's traffic.
Routers may been configured with the ATM address of
at least one MARS. Endpoints MAY choose to query maintain a table of ATM
addresses, representing alternative MARSs that will be contacted in
the event that normal operation with the original MARS for this information, rather
than multicasting IGMP queries is deemed to 224.0.0.1 and incurring
have failed. It is assumed that this table orders the
associated cost of setting up a VC to all systems ATM addresses
in descending order of preference.
An endpoint will typically decide there are problems with the cluster.
The query is issued by sending MARS
when:
- It fails to establish a MARS_GROUPLIST_REQUEST point to point VC to the MARS.
MARS_GROUPLIST_REQUEST is built from a MARS_JOIN, but it
- MARS_REQUESTs fail (section 5.1.1).
- MARS_JOIN/MARS_LEAVEs fail (section 5.2.2).
- It has an
operation code of 20 (ar$op = 20). A single <min,max> pair MUST be
provided (ar$pnum = 1), and it specifies the range of groups not received a MARS_REDIRECT_MAP in the last 4 minutes.
(If it is able to discern which connection represents
ClusterControlVC, it may also use connection failures on this VC to
indicate problems with the querying cluster member is interested.
The MARS).
5.4.1 First response from the to MARS problems.
The first response is to assume a MARS_GROUPLIST_REPLY, carrying transient problem with the MARS
being used at the time. The cluster member should wait a list random
period of time between 1 and 10 seconds before attempting to re-
connect and re-register with the multicast groups within MARS. If the specified <min,max> block registration MARS_JOIN
is successful then:
The cluster member MUST then proceed to rejoin every group that
its local higher layer protocol(s) have Layer 3 members. A group joined. It is noted in this list if one or more
of the MARS_JOINs recommended
that generated its mapping entry in the MARS
contained a set ar$layer3grp flag.
MARS_GROUPLIST_REPLYs are transmitted back to the querying random delay between 1 and 10 seconds be inserted before
attempting each MARS_JOIN.
The cluster member on the VC used to send the MARS_GROUPLIST_REQUEST.
MARS_GROUPLIST_REPLY is derived from MUST initiate the MARS_MULTI, revalidation of every
multicast group it may have
multiple parts if needed, and is received in was sending to (as though a similar manner.
Data:
ar$hrd 16 bits Hardware type ( 19 decimal, 0x13 hex)
ar$pro 16 bits Protocol type
ar$shtl 8 bits Type & length of source ATM sequence number (q)
ar$sstl 8 bits Type & length of source ATM subaddress (r)
ar$op 16 bits Operation code (MARS_GROUPLIST_REPLY = 21
decimal)
ar$spln 8 bits Length of source protocol address (s)
ar$thtl 8 bits Unused - set to zero.
ar$tstl 8 bits Unused - set to zero.
ar$tpln 8 bits Length
jump had been detected, section 5.1.5).
The rejoin and revalidation procedure must not disrupt the cluster
member's use of target multicast group address (z) multipoint VCs that were already open at the time
of the MARS failure.
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ar$tnum 16 bits Number of group addresses returned (N).
ar$seqxy 16 bits Boolean flag x
If re-registration with the current MARS fails, and sequence number y.
ar$msn 32 bits there are no
backup MARS Sequence Number.
ar$sha qoctets source ATM number (E.164 or ATM Forum NSAPA).
ar$ssa roctets source ATM subaddress (ATM Forum NSAPA).
ar$spa soctets source protocol address
ar$mgrp.1 zoctets Group address addresses configured, the cluster member MUST wait for at
least 1
[.......]
ar$mgrp.N zoctets Group minute before repeating the re-registration procedure. It is
RECOMMENDED that the cluster member signals an error condition in
some locally significant fashion.
This procedure may repeat until network administrators manually
intervene or the current MARS returns to normal operation.
5.4.2 Connecting to a backup MARS.
If the re-registration with the current MARS fails, and other MARS
addresses has been configured, the next MARS address N
ar$seqxy on the list is coded as for
chosen to be the MARS_MULTI - multiple
MARS_GROUPLIST_REPLY components are transmitted current MARS, and received using the same algorithm as cluster member immediately
restarts the re-registration procedure described in section 5.1.1 for MARS_MULTI. The
only difference 5.4.1. If
this is succesful the cluster member will resume normal operation
using the new MARS. It is RECOMMENDED that group address are being returned rather than
ATM addresses.
As the cluster member signals
a warning of this condition in some locally significant fashion.
If the attempt at re-registration with the new MARS fails, the
cluster member MUST wait for MARS_MULTIs, if an error occurs at least 1 minute before chosing the
next MARS address in the reception table and repeating the procedure. If the
end of a multi
part MARS_GROUPLIST_REPLY the whole thing MUST be discarded and table has been reached, the
MARS_GROUPLIST_REQUEST re-issued. (This includes cluster member starts again at
the ar$msn value
being constant.)
Note top of the table (which should be the original MARS that the ability to generate MARS_GROUPLIST_REQUEST messages,
and receive MARS_GROUPLIST_REPLY messages, is not required for
general host interface implementations. It is optional for interfaces
being implemented to support layer 3 multicast forwarding engines.
However,
cluster member started with).
In the worst case scenario this functionality MUST be supported by both Class I will result in cluster members
looping through their table of possible MARS addresses until network
administrators manually intervene.
5.4.3 Dynamic backup lists, and
Class II MARS.
5.4 Support for redundant/backup soft redirects.
To support some level of autoconfiguration, a MARS entities.
Endpoints are assumed to have been configured with message is defined
that allows the ATM address of
at least one MARS. Endpoints MAY choose current MARS to maintain broadcast on ClusterControlVC a table
of ATM
addresses, representing alternative MARSs backup MARS addresses. When this message is received, cluster
members that will be contacted in maintain a list of backup MARS addresses MUST insert
this information at the event that normal operation with top of their locally held list (i.e. the
information provided by the original MARS is deemed to has a higher preference than
addresses that may have failed. been manually configured into the cluster
member).
The message is MARS_REDIRECT_MAP. It is assumed based on a single MARS_MULTI,
but with an operation type code of 22 decimal. The source hardware
address information MUST be that this table orders the ATM addresses
in descending order of preference.
An endpoint will typically decide there are problems with the MARS
when:
- It fails to establish a point to point VC to MARS, and the MARS.
- MARS_REQUESTs fail (section 5.1.1).
- MARS_JOIN/MARS_LEAVEs fail (section 5.2.2).
(If source protocol
address field MUST be null (ar$spln = 0, and no space allocated).
The target protocol address MUST be null (ar$tpln = 0, and no space
allocated). If a multi-part MARS_REDIRECT_MAP begins arriving it
should be reassembled and accepted. If a part is able to discern which connection represents
ClusterControlVC, it may also use connection failures on this VC to
indicate problems with lost, the MARS). entire
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5.4.1 First response to
message should simply be discarded.
This message is transmitted regularly by the MARS problems.
The first response (it MUST be
transmitted at least every 2 minutes, it is RECOMMENDED that it is
transmitted every 1 minute).
In addition to assume a transient problem keeping cluster members updated with the recommended
list of backup MARSs, the MARS_REDIRECT_MAP is used to force cluster
members to 'soft redirect' from one MARS to another. If the first ATM
address contained in a MARS_REDIRECT_MAP is not the address of the
MARS currently being used at by a cluster member, the time. The cluster member should wait
MUST initiate the following:
- open a random
period of time between 1 and 10 seconds before attempting point to point VC to re-
connect and re-register with the MARS. first ATM address.
- attempt a registration (section 5.2.3).
If the registration MARS_JOIN
is successful then:
The succeeds, the cluster member MUST shuts down its point
to point VC to the current MARS (if it had one open), and then proceed
proceeds to rejoin every group that use the newly opened point to point VC as its local higher layer protocol(s) have joined. It is recommended
that a random delay between 1 and 10 seconds be inserted before
attempting each MARS_JOIN. connection
to the 'current MARS'. The cluster member MUST initiate does NOT attempt to rejoin
the revalidation of every
multicast group groups it was is a member of, or revalidate groups it is currently
sending to (as though to.
This is termed a sequence number
jump had been detected, section 5.1.5).
The rejoin 'soft redirect' because it avoids the extra
rejoining and revalidation procedure must not disrupt the cluster
member's use of multipoint VCs processing that were already open at the time
of the occurs when a MARS failure.
If re-registration with failure
is being recovered from. It assumes some external synchronisation
mechanisms exist between the current MARS fails, old and there are no
backup new MARS addresses configured, - mechanisms that are
outside the scope of this specification.
Some level of trust is required before initiating a soft redirect. A
cluster member MUST wait for at
least 1 minute before repeating the re-registration procedure. It is
RECOMMENDED check that the cluster member signals an error condition in
some locally significant fashion.
This procedure may repeat until network administrators manually
intervene or the current MARS returns to normal operation.
5.4.2 Connecting to a backup MARS.
If the re-registration with calling party at the current MARS fails, and other MARS
addresses has been configured, end of
the next MARS address VC on which the list MARS_REDIRECT_MAP arrived (supposedly
ClusterControlVC) is
chosen to be the current MARS, and in fact the cluster member immediately
restarts node it trusts as the re-registration procedure described in section 5.4.1. If current MARS.
Additional applications of this function are for further study.
5.5 Data path LLC/SNAP encapsulations.
The following LLC/SNAP encapsulation method is succesful the cluster member will resume normal operation
using default to be used
when multicasting layer 3 packets.
[0xAA-AA-03][0x00-00-5E][0x00-01][Extended Layer 3 packet]
(The OUI of 0x00-00-5E belongs to IANA. The PID of 0x00-01 under the new MARS. It is RECOMMENDED
IANA space indicates that the cluster member signals a warning of this condition specially extended layer 3 packet is
being carried.)
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The extended layer 3 packet is encoded in some locally significant fashion.
If the attempt at re-registration following manner:
[pkt$cmi][pkt$pro][Original Layer 3 packet]
The first 2 octets (pkt$cmi) carry the Cluster Member ID (CMI)
assigned when an endpoint registers with the new MARS fails, (section 5.2.3).
The second 2 octets (pkt$pro) indicate the
cluster member MUST wait for at least 1 minute before chosing protocol type of the
next MARS address
packet carried in the table and repeating remainder of the procedure. If payload. This is copied from
the
end of ar$pro field used in the table has been reached, MARS control messages.
For example, an IPv4 packet would be transmitted as:
[0xAA-AA-03][0x00-00-5E][0x00-01][pkt$cmi][0x800][IPv4 packet]
The CMI is copied into every multicast packet transmitted with the cluster member starts again at
above LLC/SNAP header. When an endpoint interface receives a packet
with the top of LLC/SNAP header shown above it compares the CMI field with
its own Cluster Member ID for that protocol. The packet is discarded
silently if they match. Otherwise the table (which should be packet is accepted for
processing by the original MARS that local protocol entity identified by the
cluster member started with).
In pkt$pro
field.
(This approach is required to allow the worst case scenario this will result in cluster members
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looping through their table filtering out of reflected
packets that are possible MARS addresses until network
administrators manually intervene.
5.4.3 Dynamic backup lists, and soft redirects.
To support some level of autoconfiguration, when a MARS message group is defined
that being supported by an MCS.)
The different LLC/SNAP codepoints for unicast and multicast packet
transmission allows the current MARS a single IP/ATM interface to broadcast support both by
demuxing on ClusterControlVC a table
of backup the LLC/SNAP header.
6. The MARS addresses. When this message is received, cluster
members that maintain in greater detail.
Section 5 implies a list of backup MARS addresses MUST insert
this information at the top of their locally held list (i.e. lot about the
information provided MARS's basic behaviour as observed
by cluster members. This section summarises the behaviour of the MARS has a higher preference than
addresses
for groups that may have been manually configured into the cluster
member).
The message is MARS_REDIRECT_MAP. It is based on are VC mesh based, and describes how a single MARS_MULTI,
but with MARSs
behaviour changes when an operation type code of 22 decimal. The source hardware
address information MUST be that of the MARS, and the source protocol
address field MUST be null (ar$spln = 0, and no space allocated). MCS is registered to support a group.
The target protocol address MUST MARS is intended to be null (ar$tpln = 0, and no space
allocated). If a multi-part MARS_REDIRECT_MAP begins arriving it
should be reassembled multiprotocol entity - all its mapping
tables, CMIs, and accepted. If a part is lost, the entire
message should simply control VCs MUST be discarded.
This message is transmitted regularly by managed within the context of
the ar$pro field in incoming MARS (it MUST be
transmitted at least every 2 minutes, messages. For example, a MARS
supports completely separate ClusterControlVCs for each layer 3
protocol (ar$pro type) that it is RECOMMENDED registering members for. If a MARS
receives messages with an ar$pro type that it does not support, the
message is
transmitted every 1 minute). dropped.
In addition to keeping cluster members updated with general the recommended
list of backup MARSs, MARS treats protocol addresses as arbitrary byte
strings. For example, the MARS_REDIRECT_MAP MARS will not apply IPv4 specific 'class'
checks to addresses supplied under ar$pro = 0x800. It is used sufficient
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for the MARS to force cluster
members simply assume that endpoints know how to 'soft redirect' from one interpret
the protocol addresses that they are establishing and releasing
mappings for.
6.1 Basic interface to Cluster members.
The following MARS messages are used or required by cluster members:
11 MARS_REQUEST
12 MARS_MULTI
14 MARS_JOIN
15 MARS_LEAVE
16 MARS_NAK
20 MARS_GROUPLIST_REQUEST
21 MARS_GROUPLIST_REPLY
22 MARS_REDIRECT_MAP
6.1.1 Response to another. If the first MARS_REQUEST.
Except as described in section 6.2, if a MARS_REQUEST arrives whose
source ATM address contained does not match that of any registered Cluster
member the message MUST be dropped and ignored.
6.1.2 Response to MARS_JOIN and MARS_LEAVE.
When a registration MARS_JOIN arrives (described in a MARS_REDIRECT_MAP is not the address of section 5.2.3)
the MARS currently being used by a cluster member, performs the cluster member
MUST initiate following actions:
- Adds the following: node to ClusterControlVC.
- open Allocates a point to point VC to new Cluster Member ID (CMI).
- Inserts the first ATM address. new CMI into the ar$cmi field of the MARS_JOIN.
- attempt a registration (e.g. Retransmits the MARS_JOIN for "0.0.0.0"). back privately.
If the registration succeeds, node is already a registered member of the cluster member shuts down associated
with the specified protocol type then its point
to point VC to existing CMI is simply
copied into the current MARS (if it had one open), MARS_JOIN, and then
proceeds to use the newly opened point to point VC as its connection MARS_JOIN retransmitted back to
the 'current MARS'. node. A single node may register multiple times if it supports
multiple layer 3 protocols. The cluster member does NOT attempt to rejoin CMIs allocated by the groups it is MARS for each
such registration may or may not be the same.
The retransmitted registration MARS_JOIN must NOT be sent on
ClusterControlVC. If a cluster member of, or revalidate groups it is currently
sending to.
This is termed issues a 'soft redirect' because deregistration
MARS_LEAVE it avoids the extra
rejoining and revalidation processing that occurs when a MARS failure too is being recovered from. It assumes some external synchronisation
mechanisms exist between the old retransmitted privately.
All other MARS_JOIN and new MARS - mechanisms that MARS_LEAVE messages are retransmitted on
ClusterControlVC (after successfully performing any required database
updates) exactly as they arrived. The MARS retransmits MARS_JOIN and
MARS_LEAVE messages even if they result in no change to the database.
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outside the scope of this specification.
Some level of trust is required before initiating a soft redirect. A
cluster member
MARS_JOIN or MARS_LEAVE messages MUST check that the calling party arrive at the other end of
the VC on which MARS with
ar$flags.copy set to 0, otherwise the MARS_REDIRECT_MAP arrived (supposedly
ClusterControlVC) message is in fact the node it trusts silently ignored.
All outgoing MARS_JOIN or MARS_LEAVE messages have ar$flags.copy set
to 1.
ar$flags.layer3grp (section 5.3) MUST be ignored (and treated as the current MARS.
Additional applications of this function are for further study.
5.5 LLC/SNAP encapsulations for transmit and receive.
Network administrators who require only VC mesh support
reset) for their
multicasting would use MARS_JOINs specifying more than a Class I MARS. In this case single group. If a
MARS_JOIN is received that contains more than one <min,max> pair, the default
MARS MUST ignore the second and subsequent pairs.
An additional IPv4 specific behaviour exists - if a node issues a
MARS_LEAVE for
data traffic carried on point to multipoint VCs address "224.0.0.1" (the 'all systems' group) it is LLC/SNAP
encapsulation with a header appropriate
assumed to have ceased multicast support completely. All references
to the protocol being
carried. For IP traffic this node MUST be eliminated from any other IPv4 groups it is defined a
member of in RFC 1483 as:
[0xAA-AA-03][0x00-00-00][0x08-00][IP packet]
(LLC) (OUI) (PID)
Network administrators who require the ability to use MCSs on certain
multicast groups will use a Class II MARS. They will also require database. However, the endpoint interfaces that detect and filter out reflected packets.
This is achieved by adding another field NOT released as a
leaf node from ClusterControlVC (this only occurs upon receipt of information to a
deregistration MARS_LEAVE).
If the
encapsulation MARS receives a deregistration MARS_LEAVE (described in
section 5.2.3) that is already wrapped around layer 3 data packets.
The information to member's ATM address MUST be included is the Cluster Member Identifier
(CMI), removed from all
groups for which is allocated during registration by both Class I it may have joined, dropped from ClusterControlVC,
and
Class II MARSs (section 5.2.3).
When a packet is transmitted the CMI is inserted into released.
If the
encapsulation. When MARS receives an ERR_L_RELEASE on ClusterControlVC indicating
that a packet is received, if cluster member has disconnected, that member's ATM address
MUST be removed from all groups for which it may have joined, and the
CMI carried along
with released.
6.1.3 Generating MARS_REDIRECT_MAP.
A MARS_REDIRECT_MAP message (described in section 5.4.3) MUST be
regularly transmitted on ClusterControlVC. It is RECOMMENDED that
this occur every 1 minute, and it matches MUST occur at least every 2
minutes. If the CMI MARS has no knowledge of other backup MARSs serving
the local interface cluster, it MUST include its own address as the packet is simply
dropped. only entry in the
MARS_REDIRECT_MAP message (in addition to filling in the source
address fields).
The recommended encapsulation is:
[Editors note: This design and use of backup MARS entities is a placeholder for beyond the results scope of
this document, and will be covered in future work.
6.1.4 Cluster Sequence Numbers.
The Cluster Sequence Number (CSN) is described in section 5.1.4, and
is carried in the WG
discussion ar$msn field of MARS messages being sent to cluster
members (either out ClusterControlVC or on an individual VC). The
MARS increments the encapsulation options. Check draft-armitage-
ipatm-encaps-01.txt or later version. CSN every time a message is sent on
ClusterControlVC. The WG current CSN is expected to come
up with some text that will simply be dropped copied into this section.]
Using a different LLC/SNAP value to identify packets containing the
CMI allows endpoints to separate and simultaneously support both old
and new encapsulated traffic. ar$msn field of
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6. The MARS in greater detail.
As noted in the overview of section 4, there are two types of MARS
defined in this specification. The Class I
MARS is messages being sent to cluster members, whether out
ClusterControlVC or on a superset of private VC.
A MARS should be carefully designed to minimise the
RFC1577 ARP Server, and is capable possibility of managing clusters where
the CSN jumping unecessarily. Under normal operation only VC
meshes are used cluster
members affected by transient link problems will miss CSN updates and
be forced to achieve intra-cluster multicasting.
The Class II MARS is a superset of revalidate. If the Class I MARS, with extensions
that allow MARS itself glitches, it to transparently introduce multicast servers into the
data paths established by endpoints that comply with the
specifications in section 5. (It is worth noting here that complete
compliance will be
innundated with section 5 includes being able to use the new
encapsulation carrying the Cluster Member ID. Networks built around requests for a
Class I MARS may choose period as every cluster member
attempts to initially not fully comply with section 5
in revalidate.
Calculations on the CSN MUST be performed as unsigned 32 bit
arithmetic.
One implication of this respect, although it mechanism is RECOMMENDED that they do.)
The the MARS is intended to be a multiprotocol entity - all should serialize
its mapping
tables processing of 'simultaneous' MARS_REQUEST, MARS_JOIN and
MARS_LEAVE messages. Join and control VCs MUST Leave operations should be managed queued
within the context of the
ar$pro field in incoming MARS messages. For example, a MARS supports
completely separate ClusterControlVCs for each layer 3 protocol
(ar$pro type) that it is registering members for. If a MARS receives
messages along with an ar$pro type that it does MARS_REQUESTS, and not support, the message is
dropped.
6.1 Class I MARS requirements.
A Class I MARS must understand and/or generate processed until all
the following MARS
messages:
11 reply packets of a preceeding MARS_REQUEST
12 MARS_MULTI
14 MARS_JOIN
15 MARS_LEAVE
16 MARS_NAK
20 MARS_GROUPLIST_REQUEST
21 MARS_GROUPLIST_REPLY
22 have been transmitted.
The transmission of MARS_REDIRECT_MAP
Section 5 covers how these messages are used or reacted to by
endpoints within a cluster. This section provides should also be similarly
queued.
(The regular transmission of MARS_REDIRECT_MAP serves a brief summary secondary
purpose of
how allowing cluster members to track the Class I MARS uses CSN, even if they
miss an earlier MARS_JOIN or reacts MARS_LEAVE.)
6.2 MARS interface to them. Multicast Servers (MCS).
When a registration MARS_JOIN arrives (e.g. for address "0.0.0.0" if
ar$pro = 0x800 [IPv4]) the MARS performs returns the following:
- Adds actual addresses of group members, the node
endpoint behaviour described in section 5 results in all groups being
supported by meshes of point to ClusterControlVC.
- Allocates a new Cluster Member ID (CMI).
- Inserts multipoint VCs. However, when MCSs
register to support particular layer 3 multicast groups the new CMI MARS
modifies its use of various MARS messages to fool endpoints into
using the ar$cmi field of MCS instead.
The following MARS messages are associated with interaction between
the MARS_JOIN. MARS and MCSs.
13 MARS_MSERV
17 MARS_UNSERV
18 MARS_SJOIN
19 MARS_SLEAVE
The following MARS messages are treated in a slightly different
manner when MCSs have registered to support certain group addresses:
11 MARS_REQUEST
14 MARS_JOIN
15 MARS_LEAVE
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- Retransmits the MARS_JOIN back privately.
If
A MARS must keep two sets of mappings for each layer 3 group using
MCS support. The original {layer 3 address, ATM.1, ATM.2, ... ATM.n}
mapping (now termed the node 'host map', although it includes routers) is already
augmented by a registered member of the cluster (given the
ar$pro value in the MARS_JOIN) then its CMI parallel {layer 3 address, server.1, server.2, ....
server.K} mapping (the 'server map'). It is simply copied into assumed that no ATM
addresses appear in both the
MARS_JOIN, server and the MARS_JOIN retransmitted back to the node. A
single node may register multiple times if it supports multiple layer
3 protocols. The retransmitted MARS_JOIN must NOT be sent on
ClusterControlVC. (If a cluster member issues a MARS_LEAVE host maps for the
registration 'special' address same
multicast group. Typically K will be 1, but it too is retransmitted privately.)
All other MARS_JOIN and MARS_LEAVE messages are retransmitted on
ClusterControlVC (after successfully performing any required database
updates) exactly as they arrived. The MARS retransmits MARS_JOIN and
MARS_LEAVE messages even will be larger if they result in no change
multiple MCSs are configured to the database.
The ar$layer3grp flag (section 5.3) MUST be ignored (and treated as
reset) for MARS_JOINs specifying more than support a single given group. If
The MARS also maintains a
MARS_JOIN is received that contains more than one <min,max> pair, point to multipoint VC out to any MCSs
registered with it, called ServerControlVC (section 6.2.3). This
serves an analogous role to ClusterControlVC, allowing the MARS MUST ignore to
update the second MCSs with group membership changes as they occur. A MARS
MUST also send its regular MARS_REDIRECT_MAP transmissions on both
ServerControlVC and subsequent pairs.
An additional IPv4 specific behaviour exists - if ClusterControlVC.
6.2.1 Response to a node issues MARS_REQUEST if MCS is registered.
When the MARS receives a
MARS_LEAVE MARS_REQUEST for an address "224.0.0.1" (the 'all systems' group) it is
assumed to have ceased multicast support completely. All references
to this node MUST be eliminated from any other IPv4 groups that has both
host and server maps it generates a response based on the identity of
the request's source. If the requestor is a member of in the database. Finally, server map
for the endpoint requested group then the MARS returns the contents of the
host map in a sequence of one or more MARS_MULTIs. Otherwise, if the
source is released as a
leaf node from ClusterControlVC.
If valid cluster member, the MARS receives an ERR_L_RELEASE on ClusterControlVC indicating
that returns the contents of
the server map in a sequence of one or more MARS_MULTIs. If the
source is neither a cluster member, nor a member has died, of the server map
for the group, the request is dropped and ignored.
Servers use the host map to establish a basic distribution VC for the
group. Cluster members will establish outgoing multipoint VCs to
members of the group's server map, without being aware that member's ATM address MUST their
packets will not be
removed from all groups for which it may have joined.
As mentioned in section 4, going directly the MARS only needs multicast group's members.
6.2.2 MARS_MSERV and MARS_UNSERV messages.
MARS_MSERV and MARS_UNSERV are identical to interpret the
protocol address supplied in MARS messages on MARS_JOIN message.
An MCS uses a few odd occasions.
In general the MARS MUST treat protocol addresses as arbitrary byte
strings. For example, the MARS MUST NOT apply IPv4 specific 'class'
checks to addresses supplied under ar$pro = 0x800 MARS_MSERV with a <min,max> pair of <X,X> to see if they
really are Class D or not. It is sufficient for specify
the MARS to simply
assume multicast group X that endpoints know how it is willing to interpret support. A single group
MARS_UNSERV indicates the protocol addresses group that they are registering the MCS is no longer willing to
support. The operation code for MARS_MSERV is 13 (decimal), and deregistering mappings for.
A MARS_REDIRECT_MAP
MARS_UNSERV is 17 (decimal).
When operating on specific groups ar$flags.register MUST be zero.
When an MCS issues a MARS_MSERV for a specific group the message (described in section 5.4.3) MUST
be
regularly transmitted on ClusterControlVC. It is RECOMMENDED that
this occur every 1 minute, dropped and it MUST occur at least every 2
minutes. If ignored if the MARS source has no knowledge of other backup MARSs serving not already registered with
the cluster, it MUST include its own address MARS as a multicast server (section 6.2.3). Otherwise, the only entry in the
MARS_REDIRECT_MAP message. The design and use of backup MARS entities
is beyond
adds the scope of this specification, and will be covered in
future work. new ATM address to the server map for the specified group,
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possibly constructing a new server map if this is carried in the ar$msn field of first MCS for
the group.
When an MCS issues a MARS_UNSERV the MARS messages removes its ATM address
from the server maps for each specified group, deleting any server
maps that end up being null after the operation.
Both of these messages are sent to cluster
members (either out ClusterControlVC or the MARS over a point to point VC
(between MCS and MARS). After processing, they are retransmitted on an individual VC).
ServerControlVC to allow other MCSs to note the new node.
The
MARS increments operation code is then changed to MARS_JOIN or MARS_LEAVE
respectively, and another copy of the CSN every time a message is sent also transmitted on
ClusterControlVC. The current CSN is copied This fools the cluster members into thinking a new
leaf node as been added to (or dropped from) the ar$msn field of group specified. In
the retransmitted MARS_JOIN/LEAVE ar$flags.layer3grp MUST be zero,
ar$flags.copy MUST be one, and ar$flags.register MUST be zero.
The MARS retransmits redundant MARS_MSERV and MARS_UNSERV messages being sent to cluster members, whether out
ClusterControlVC
onto ServerControlVC, generates the appropriate MARS_JOIN or
MARS_LEAVE messages on ClusterControlVC, but takes no further action.
It is assumed that at least one MCS will have MARS_MSERV'ed a private VC.
A MARS should be carefully designed to minimise the possibility of group
before the CSN jumping unecessarily. Under normal operation only first cluster
members affected by transient link problems will miss CSN updates and
be forced to revalidate. member joins it. If a MARS_MSERV arrives for
a group that has a non-null host map but no server map the default
response of the MARS itself glitches, it will be
innundated with requests for a period as every cluster member
attempts to revalidate.
Calculations on silently drop the CSN MUST be performed as unsigned 32 bit
arithmetic, MARS_MSERV without
any further action. The MCS attempting to ensure no glitches when support the counters roll over.
(The regular transmission of MARS_REDIRECT_MAP serves group will
eventually flag an error after repeated MARS_MSERVs fail.
The last or only MCS for a secondary
purpose of allowing cluster members group MAY choose to track issue a MARS_UNSERV
while the CSN, even if they
miss an earlier MARS_JOIN or MARS_LEAVE.)
One implication of this mechanism is that group still has members. When the MARS should serialize
its processing of 'simultaneous' MARS_REQUEST, MARS_JOIN and
MARS_LEAVE messages. Join and Leave operations should be queued
within MARS_UNSERV is processed
by the MARS along with MARS_REQUESTS, and not processed until all the reply packets of a preceeding MARS_REQUEST have been transmitted.
The transmission of MARS_REDIRECT_MAP should also 'server map' will be similarly
queued.
6.2 Class II MARS requirements. deleted. When using the services of associated
MARS_LEAVE is issued on ClusterControlVC, all cluster members with a Class I MARS,
VC open to the endpoint behaviour
described in MCS for that group will close down the VC (in
accordance with section 5 results in all groups being supported by
meshes of point to multipoint VCs. Section 3 discusses some of 5.1.4, since the
reasons why network administrators and designers may wish MCS was their only leaf
node). When cluster members subsequently find they need to utilise
MCSs transmit
packets to achieve their intra-cluster multicasting instead. The Class
II the group, they will begin again with the
MARS_REQUEST/MARS_MULTI sequence to establish a new VC. Since the
MARS includes all will have deleted the functionality of server map, this will result in the Class I, but modifies
its use of various MARS messages host
map being return, and the group reverts to fool endpoints into using MCSs
where needed.
The additional MARS messages being supported by a Class II MARS are
primarily associated with iteraction between VC
mesh.
A clean mechanism for the MARS and reverse process - transitioning a group
from a VC mesh to MCS supported while the MCSs.
13 MARS_MSERV
17 MARS_UNSERV
18 MARS_SJOIN
19 MARS_SLEAVE group is active - is a
subject for further study.
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6.2.3 Registering a Multicast Server (MCS).
Section 5.2.3 describes how endpoints register as cluster members,
and hence get added as leaf nodes to ClusterControlVC. The following same
approach is used to register endpoints that intend to provide MCS
support.
Registration with the MARS messages are treated in occurs when an endpoint issues a slightly different
manner:
11 MARS_REQUEST
14 MARS_JOIN
15 MARS_LEAVE
A Class II MARS must keep two sets of mappings for each layer 3 group
using
MARS_MSERV with ar$flags.register set to one. Upon registration the
endpoint is added as a leaf node to ServerControlVC, and the
MARS_MSERV is returned to the MCS support. privately.
The original {layer 3 address, ATM.1, ATM.2, ...
ATM.n} mapping (now termed MCS retransmits this MARS_MSERV until it confirms that the 'host map', although MARS
has received it includes
routers) is augmented (by receiving a copy back, in an analogous way to the
mechanism described in section 5.2.2 for reliably transmitting
MARS_JOINs).
The ar$cmi field in MARS_MSERVs MUST be set to zero by both MCS and
MARS.
An MCS may also choose to de-register, using a parallel {layer 3 address, server.1,
server.2, .... server.K} mapping (the 'server map'). It is assumed MARS_UNSERV with
ar$flags.register set to one. When this occurs the MARS MUST remove
all references to that no ATM addresses appear MCS in both all servermaps associated with the server and host maps for
protocol (ar$pro) specified in the MARS_UNSERV.
Note that multiple logical MCSs may share the same multicast group. Typically K will be 1, but it will physical ATM
interface, provided that each MCS uses a separate ATM address (e.g. a
different SEL field in the NSAP format address). In fact, an MCS may
share the ATM interface of a node that is also a cluster member
(either host or router), provided each logical entity has a different
ATM address.
A MARS MUST be larger if capable of handling a multi-entry servermap. However,
the possible use of multiple MCSs are configured registering to support the same
group is a subject for further study. In the absence of an MCS
synchronisation protocol a system administrator MUST NOT allow more
than one logical MCS to register for a given group.
6.2.4 Modified response to MARS_JOIN and MARS_LEAVE.
The existence of MCSs supporting some groups but not others requires
the MARS to modify its distribution of single and block join/leave
updates to cluster members. The MARS also maintains a point to multipoint VC out adds two new messages -
MARS_SJOIN and MARS_SLEAVE - for communicating group changes to any MCSs
registered with it, called ServerControlVC (section 6.2.3). This
serves an analogous role to ClusterControlVC, allowing the MARS
over ServerControlVC.
The MARS_SJOIN and MARS_SLEAVE messages are identical to
update the MCSs MARS_JOIN,
with group membership changes as they occur. A Class
II MARS MUST also send its regular MARS_REDIRECT_MAP transmissions on
both ServerControlVC operation codes 18 and ClusterControlVC.
6.2.1 Class II MARS response to a MARS_REQUEST. 19 (decimal) respectively.
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When the MARS receives a MARS_REQUEST cluster member issues MARS_JOIN or MARS_LEAVE for an address that has both
host and server maps it generates a response based on single
group, the identity of MARS checks to see if the request's source. group has an associated server
map. If the requestor is specified group does not have a member of the server map
for the requested group then the MARS returns the contents of
simply retransmits the
host map in a sequence of one MARS_JOIN or more MARS_MULTIs. Otherwise the MARS
returns the contents of the server map in MARS_LEAVE on ClusterControlVC.
However, if a sequence of one or more
MARS_MULTIs.
Servers use the host server map to establish a basic distribution VC exists for the
group. Cluster members will establish outgoing multipoint VCs to
members group a new set of the group's server map, without being aware that their
packets will not be going directly the multicast group's members.
6.2.2 MARS_MSERV and MARS_UNSERV messages.
MARS_MSERV and MARS_UNSERV actions
are identical to the MARS_JOIN message.
An MCS uses a MARS_MSERV with a <min,max> pair taken.
A copy of <X,X> to specify the multicast group X that it MARS_JOIN/LEAVE is willing to support. A single group
MARS_UNSERV indicates made with type MARS_SJOIN or
MARS_SLEAVE as appropriate, and transmitted on ServerControlVC.
This allows the group that MCS(s) supporting the MCS is no longer willing group to
support. note the new member
and update their data VCs.
The operation code for MARS_MSERV original message's ar$pnum field is 13 (decimal), set to 0, and
MARS_UNSERV it is 17 (decimal).
When an MCS issues a MARS_MSERV the MARS adds
transmitted back using the new ATM address VC it arrived on (rather than
ClusterControlVC).
(Section 5.2.2 requires cluster members have a mechanism to
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the server map for reception of their message by the specified group, possibly constructing a new
server map if MARS. For mesh supported
groups, using ClusterControlVC serves dual purpose of providing this is the first MCS for the group.
confirmation and distributing group update information. When an MCS issues a MARS_UNSERV the MARS removes its ATM address
from the server maps group
is MCS supported, there is no reason for each specified group, deleting any server
maps that end up being all cluster members to
process null after the operation.
Both of these join/leave messages on ClusterControlVC, so they are
sent to back on the MARS over a point to point private VC
(between MCS between cluster member and MARS). After processing, they are retransmitted on
ServerControlVC MARS.)
Receipt of a block MARS_JOIN (e.g. from a router coming on-line) or
MARS_LEAVE requires a more complex response. The single <min,max>
block may simultaneously cover mesh supported and MCS supported
groups. However, cluster members only need to allow other be informed of the
mesh supported groups that the endpoint has joined. Only the MCSs
need to note know if the new node. endpoint is joining any MCS supported groups.
The operation code solution is then changed to modify the MARS_JOIN or MARS_LEAVE
respectively, and another that is
retransmitted on ClusterControlVC. The following action is taken:
A copy of the message MARS_JOIN/LEAVE is also made with type MARS_SJOIN or
MARS_SLEAVE as appropriate, and transmitted on
ClusterControlVC. ServerControlVC.
This fools allows the cluster members into thinking a new
leaf node as been added to (or dropped from) MCS(s) supporting the group specified. The
ar$layer3grp flag MUST be reset for to note the retransmitted
MARS_JOIN/LEAVE.
The MARS retransmits but otherwise ignores redundant MARS_MSERV membership
change and
MARS_UNSERV messages.
It update their outgoing point to multipoint VCs.
The <min,max> block supplied in the original MARS_JOIN/LEAVE is assumed that at least one MCS will have MARS_MSERV'ed
replaced with a group
before 'hole punched' set of zero or more <min,max>
pairs. The 'hole punched' set of <min,max> pairs covers the first cluster member joins it. If a MARS_MSERV arrives for
a group that has a non-null host map
entire address range specified by the original <min,max> pair, but no server map
excludes those addresses/groups supported by MCSs.
If the default
response of hole-punched set contains 1 or more <min,max> pair, the MARS will be to silently drop
MARS_JOIN/LEAVE is transmitted on ClusterControlVC.
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If the MARS_MSERV without
any further action. The MCS attempting hole-punched set is empty, the ar$pnum field is set to support
zero, and the group will
eventually flag an error after repeated MARS_MSERVs fail.
The last or only MCS MARS_JOIN/LEAVE is transmitted back using the VC it
arrived on (rather than ClusterControlVC).
(Appendix A discusses some algorithms for a group MAY choose 'hole punching'.)
It is assumed that MCSs use the MARS_SJOINs and MARS_SLEAVEs to
update their own VCs out to issue a MARS_UNSERV
while the group still has actual group's members. When the MARS_UNSERV
ar$flags.layer3grp is processed
by copied over into the MARS messages transmitted by
the 'server map' will MARS. ar$flags.copy MUST be deleted. When the associated
MARS_LEAVE is issued on ClusterControlVC, all cluster members with a
VC open set to the MCS for that group will close down the VC (in
accordance with section 5.1.4, since the MCS was their only leaf
node). When cluster members subsequently find they need one, and ar$flags.register
MUST be set to transmit
packets zero.
6.2.5 Sequence numbers for ServerControlVC traffic.
In an analogous fashion to the group, they will begin again with Cluster Sequence Number, the
MARS_REQUEST/MARS_MULTI sequence to establish MARS
keeps a new VC. Since Server Sequence Number (SSN) that is incremented for every
transmission on ServerControlVC. The current value of the
MARS will have deleted SSN is
inserted into the server map, this will result in ar$msn field of every message the host
map MARS issues that
it believes is destined for an MCS. This includes MARS_MULTIs that
are being return, and the group reverts returned in response to being supported by a VC
mesh.
A clean mechanism for the reverse process - transitioning a group MARS_REQUEST from a VC mesh to an MCS, and
MARS_REDIRECT_MAP being sent on ServerControlVC. The MCS supported while must check
the group is active - MARS_REQUESTs source, and if it is a
subject for further study.
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6.2.3 Registering a Multicast Server (MCS).
Section 5.2.3 describes how endpoints register as cluster members,
and hence get added as leaf nodes to ClusterControlVC. The same
approach registered MCS the SSN is
copied into the ar$msn field, otherwise the CSN is used copied into the
ar$msn field.
MCSs are expected to register track and use the SSNs in an analogous manner to
the way endpoints that intend use the CSN in section 5.1 (to trigger revalidation
of group membership information).
A MARS should be carefully designed to provide MCS
support minimise the possibility of
the SSN jumping unecessarily. Under normal operation only MCSs that
are affected by transient link problems will miss ar$msn updates and
be forced to a Class II MARS.
Registration with revalidate. If the MARS occurs when an endpoint issues a
MARS_MSERV itself glitches it will be
innundated with requests for a protocol specific multicast group address. Upon
registration the endpoint is added period as a leaf node to ServerControlVC.
In IPv4 environments an every MCS endpoint MUST explicitly issue a
MARS_MSERV for the special address "0.0.0.0" in order attempts to register
with
revalidate.
6.3 Why global sequence numbers?
The CSN and SSN are global within the MARS. In other words, a MARS_MSERV with ar$tpln context of 4, a given protocol
(e.g. IP). They count ClusterControlVC and 8
bytes of zero starting at ar$min.1 (equivalent ServerControlVC activity
without reference to the block of
<0.0.0.0,0.0.0.0>. multicast group(s) involved. This may be
perceived as a limitation, because there is no way for cluster
members or multicast servers to isolate exactly which multicast group
they may have missed an update for. An alternative was to try and
provide a per-group sequence number.
Unfortunately per-group sequence numbers are not practical. The specific addresses signifying 'registration'
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current mechanism allows sequence information to be piggy-backed onto
MARS messages already in transit for other layer 3
protocols will defined in subsequent documents. reasons. The MCS retransmits this MARS_MSERV until it confirms ability to
specify blocks of multicast addresses with a single MARS_JOIN or
MARS_LEAVE means that the MARS
has received it (by receiving a copy back, in an analogous way single message can refer to the
mechanism described in section 5.2.2 membership change
for reliably transmitting
MARS_JOINs).
The ar$cmi multiple groups simultaneously. A single ar$msn field in MARS_MSERVs cannot
provide meaningful information about each group's sequence. Multiple
ar$msn fields would have been unwieldy.
Any MARS or cluster member that supports different protocols MUST
keep separate mapping tables and sequence numbers for each protocol.
6.4 Redundant/Backup MARS Architectures.
If backup MARSs exist for a given cluster then mechanisms are set needed
to zero by both MCS ensure consistency between their mapping tables and those of the
active, current MARS.
An MCS may also choose
(Cluster members will consider backup MARSs to de-register, using exist if they have
been configured with a MARS_UNSERV. In an
IPv4 environment table of MARS addresses, or the regular
MARS_REDIRECT_MAP messages contain a MARS_UNSERV on list of 2 or more addresses.)
The definition of an MARS-synchronization protocol is beyond the special address
current scope of "0.0.0.0"
would result in this document, and is expected to be the MARS dropping subject of
further research work. However, the MCS from ServerControlVC.
Note that multiple logical MCSs following observations may share the same physical ATM
interface, provided that each MCS uses a separate ATM address (e.g. a
different SEL field be
made:
The MARS_REDIRECT_MAP message exist, enabling one MARS to force
endpoints to move to another MARS (e.g. in the NSAP format address). In fact, an MCS may
share the ATM interface aftermath of a node that is also a cluster member
(either host or router), provided each logical entity has a different
ATM address.
6.2.4 Class II response to MARS_JOIN and MARS_LEAVE.
The existence of MCSs supporting some groups but not others requires MARS
failure, the Class II chosen backup MARS will eventually wish to modify its distribution hand
control of single and block
join/leave updates to the cluster members. The Class II over to the main MARS also adds
two new messages - MARS_SJOIN when it is
functioning properly again).
Cluster members and MARS_SLEAVE - for communicating
group changes to MCSs over ServerControlVC.
The MARS_SJOIN and MARS_SLEAVE messages are identical do not need to MARS_JOIN, start up with operation codes 18 and 19 (decimal) respectively.
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When a cluster member knowledge of
more than one MARS, provided that MARS correctly issues MARS_JOIN or MARS_LEAVE
MARS_REDIRECT_MAP messages with the full list of MARSs for a single
group, that
cluster.
Any mechanism for synchronising backup MARSs (and coping with the
aftermath of MARS checks to see if failures) should be compatible with the group has cluster
member behaviour described in this document.
7. How an associated server
map. If the specified group does not have a server map the MARS
provides MCS utilises a Class I service and simply retransmits the MARS_JOIN or
MARS_LEAVE on ClusterControlVC.
However, if MARS.
When an MCS supports a server map exists for the multicast group a new set of actions
are taken.
A copy of the MARS_JOIN/LEAVE is made with type MARS_SJOIN or
MARS_SLEAVE it acts as appropriate, and transmitted on ServerControlVC.
This allows the MCS(s) supporting a proxy cluster
endpoint for the group senders to note the new member
and update their data VCs.
The original message's ar$pnum field is set group. It also behaves in an
analogous manner to 0, and it is
transmitted back using the VC it arrived on (rather than
ClusterControlVC).
(Section 5.2.2 requires cluster members have a mechanism sender, managing a single outgoing point to
multipoint VC to confirm the reception real group members.
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Detailed description of their message by possible MCS architectures are beyond the MARS. For mesh supported
groups, using ClusterControlVC serves dual purpose
scope of providing this
confirmation and distributing group update information. When document. This section will outline the main issues.
7.1 Association with a group
is particular Layer 3 group.
When an MCS supported, there is no reason for issues a MARS_MSERV it forces all cluster members senders to
process null join/leave messages on ClusterControlVC, so they are
sent back the
specified layer 3 group to terminate their VCs on the private VC between cluster member supplied source
ATM address.
The simplest MCS architecture involves taking incoming AAL_SDUs and MARS.)
Receipt of a block MARS_JOIN (e.g. from a router coming on-line) or
MARS_LEAVE requires
simply flipping them back out a more complex response. The single <min,max>
block may simultaneously cover VC mesh supported and point to multipoint VC. Such
an MCS supported
groups. However, cluster members only need cannot support more than one group at once, as it has no way
to be informed of the VC
mesh supported differentiate between traffic destined for different groups.
Using this architecture, a physical node would provide MCS support
for multiple groups that by creating multiple logical instances of the endpoint has joined. Only
MCS, each with different ATM Addresses (e.g. a different SEL value in
the MCSs
need node's NSAPA).
A slightly more complex approach would be to know if add minimal layer 3
specific processing into the endpoint is joining any MCS supported groups.
The solution is to modify MCS. This would look inside the MARS_JOIN or MARS_LEAVE that is
retransmitted on ClusterControlVC. The following action is taken: received
AAL_SDUs and determine which layer 3 group they are destined for. A copy
single instance of the MARS_JOIN/LEAVE is made such an MCS might register its ATM Address with type MARS_SJOIN or
MARS_SLEAVE as appropriate, and transmitted on ServerControlVC.
This allows the MCS(s) supporting the group to note
the membership
change MARS for multiple layer 3 groups, and update their manage multiple independent
outgoing point to multipoint VCs.
The <min,max> block supplied VCs (one for each group).
When an MCS starts up it MUST register with the MARS as described in
section 6.2.3, identifying the original MARS_JOIN/LEAVE is
replaced protocol it supports with a 'hole punched' set of zero or more <min,max>
pairs. The 'hole punched' set the ar$pro
field of <min,max> pairs covers the
entire address range specified by MARS_MSERV. This also applies to logical MCSs, even if
they share the original <min,max> pair, but
excludes those addresses/groups supported by MCSs.
If same physical ATM interface. This is important so that
the MARS can react to the loss of an MCS when it drops off
ServControlVC. (One consequence is that 'simple' MCS architectures
end up with one ServerControlVC member per group. MCSs with layer 3
specific processing may support multiple groups while still only
registering as one member of ServerControlVC.)
An MCS MUST NOT share the hole-punched set contains 1 or more <min,max> pair, same ATM address as a cluster member,
although it may share the same physical ATM interface.
7.2 Termination of incoming VCs.
An MCS MUST terminate unidirectional VCs in the same manner as a
cluster member. (e.g. terminate on an LLC entity when LLC/SNAP
encapsulation is used, as described in RFC 1755 for unicast
endpoints.)
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MARS_JOIN/LEAVE is transmitted on ClusterControlVC.
If the hole-punched set
7.3 Management of outgoing VC.
An MCS MUST establish and manage its outgoing point to multipoint VC
as a cluster member does (section 5.1).
MARS_REQUEST is empty, used by the ar$pnum field is set MCS to
zero, and the MARS_JOIN/LEAVE is transmitted back using establish the VC it
arrived on (rather than ClusterControlVC).
(Appendix A discusses some algorithms initial leaf nodes
for 'hole punching'.)
It is assumed that MCSs use the MARS_SJOINs and MARS_SLEAVEs to
update their own VCs out MCS's outgoing point to multipoint VC. After the actual group's members.
The ar$layer3grp flag VC is copied over into the messages transmitted by
established, the MARS.
6.2.5 Sequence numbers for ServerControlVC traffic.
In an analogous fashion MCS reacts to MARS_SJOINs and MARS_SLEAVEs in the Cluster Sequence Number, a Class II
MARS keeps
same way a Server Sequence Number (SSN) that is incremented for
every transmission on ServerControlVC. The current value of the SSN
is inserted into the ar$msn field of every message the MARS issues
that it believes is destined for an MCS. This includes MARS_MULTIs
that are being returned in response cluster member reacts to a MARS_REQUEST from an MCS, MARS_JOINs and MARS_REDIRECT_MAP being sent on ServerControlVC. MARS_LEAVEs.
The MCS must
check tracks the MARS_REQUESTs source, Server Sequence Number from the ar$msn fields of
messages from the MARS, and if it is revalidates its outgoing point to
multipoint VC(s) when a registered sequence number jump occurs.
7.4 Use of a backup MARS.
The MCS uses the SSN
is copied into same approach to backup MARSs as a cluster member
(section 5.4), tracking MARS_REDIRECT_MAP messages on
ServerControlVC.
8. Support for IP multicast routers.
Multicast routers are required for the ar$msn field, otherwise propagation of multicast
traffic beyond the CSN constraints of a single cluster (inter-cluster
traffic). (There is copied into the
ar$msn field.
MCSs a sense in which they are expected to track multicast servers
acting at the next higher layer, with clusters, rather than
individual endpoints, as their abstract sources and use destinations.)
Multicast routers typically participate in higher layer multicast
routing algorithms and policies that are beyond the SSNs scope of this
memo (e.g. DVMRP [5] in an analogous manner to the way endpoints use IPv4 environment).
It is assumed that the CSN in section 5.1 (to trigger revalidation
of group membership information).
A Class II MARS should multicast routers will be carefully designed to minimise implemented over the
possibility
same sort of the SSN jumping unecessarily. Under normal operation
only MCSs IP/ATM interface that are affected by transient link problems a multicast host would use. Their
IP/ATM interfaces will miss
ar$msn updates and be forced to revalidate. If will register with the MARS itself
glitches it as a cluster
members, joining and leaving multicast groups as necessary. As noted
in section 5, multiple logical 'endpoints' may be implemented over a
single physical ATM interface. Routers use this approach to provide
interfaces into each clusters they will be innundated with requests for a period as every
MCS attempts to revalidate.
6.3 Why global sequence numbers? routing between.
The CSN and SSN are global within rest of this section will assume a simple IPv4 scenario where the context
scope of a given protocol
(e.g. IP). They count ClusterControlVC and ServerControlVC activity
without reference cluster has been limited to the multicast group(s) involved. This may be
perceived as a limitation, because there particular LIS that is no way for part
of an overlaid IP network. Not all members of the LIS are necessarily
registered cluster members or multicast servers to isolate exactly which multicast group
they (you may have missed an update for. An alternative was to try and
provide a per-group sequence number. unicast-only hosts in the
LIS).
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Unfortunately per-group sequence numbers are not practical. The
current mechanism allows sequence information to be piggy-backed onto
MARS messages already in transit for other reasons. The ability to
specify blocks of multicast addresses with
8.1 Forwarding into a single MARS_JOIN or
MARS_LEAVE means that Cluster.
If the multicast router needs to transmit a single message can refer packet to membership change
for multiple groups simultaneously. A single ar$msn field cannot
provide meaningful information about each group's sequence. Multiple
ar$msn fields would have been unwieldy.
Any MARS or a group within
the cluster member that supports different protocols MUST
keep separate mapping tables and sequence numbers for each protocol.
6.4 Redundant/Backup MARS Architectures.
If backup MARSs exist its IP/ATM interface opens a VC in the same manner as a
normal host would. Once a VC is open, the router watches for
MARS_JOIN and MARS_LEAVE messages and responds to them as a given cluster then mechanisms are needed normal
host would.
The multicast router's transmit side MUST implement inactivity timers
to ensure consistency between their mapping tables and those of shut down idle outgoing VCs, as for normal hosts.
As with normal host, the
active, current MARS.
(Cluster members will consider backup MARSs multicast router does not need to exist if they have
been configured with be a table
member of MARS addresses, or the regular
MARS_REDIRECT_MAP messages contain a list of 2 or more addresses.)
The definition of an MARS-synchronization protocol group it is beyond sending to.
8.2 Joining in 'promiscuous' mode.
Once registered and initialised, the
current scope simplest model of this document, and IPv4 multicast
router operation is expected for it to be the subject of
further research work. However, issue a MARS_JOIN encompassing the following observations may
entire Class D address space. In effect it becomes 'promiscuous', as
it will be
made:
The MARS_REDIRECT_MAP message exist enable one MARS a leaf node to force
endpoints all present and future multipoint VCs
established to move IPv4 groups on the cluster.
How a router chooses which groups to another MARS (e.g. in propagate outside the aftermath cluster is
beyond the scope of a MARS
failure, this document.
Consistent with RFC 1112, IP multicast routers may retain the chosen backup MARS will eventually wish to hand
control use of
IGMP Query and IGMP Report messages to ascertain group membership.
However, certain optimisations are possible, and are described in
section 8.5.
8.3 Forwarding across the cluster.
Under some circumstances the cluster over to the main MARS when it is
functioning properly again).
Cluster members may simply be another hop
between IP subnets that have participants in a multicast group.
[LAN.1] ----- IPmcR.1 -- [cluster/LIS] -- IPmcR.2 ----- [LAN.2]
LAN.1 and MCSs do not need to start up LAN.2 are subnets (such as Ethernet) with knowledge of
more than one MARS, provided attached hosts
that MARS correctly issues
MARS_REDIRECT_MAP messages with the full list are members of MARSs for that
cluster.
Any mechanism for synchronising backup MARSs (and coping group X.
IPmcR.1 and IPmcR.2 are multicast routers with interfaces to the
aftermath of MARS failures) should LIS.
A traditional solution would be to treat the LIS as a unicast subnet,
and use tunneling routers. However, this would not require allow hosts on the endpoint behaviour
LIS to be modified from what is described participate in this specification.
7. How an MCS utilises a Class II MARS.
Along the data path the MCS cross-LIS traffic.
Assume IPmcR.1 is a protocol independent entity, in that receiving packets promiscuously on its role LAN.1
interface. Assume further it is configured to accept AAL_SDUs from multiple sources and then
transmit them sequentially out a single point to multipoint VC. It
does not look inside the AAL_SDUs at all. However, when an MCS starts propagate multicast
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up it must register
traffic to all attached interfaces. In this case that means the LIS.
When a packet for group X arrives on its LAN.1 interface, IPmcR.1
simply sends the packet to group X on the LIS interface as a normal
host would (Issuing MARS_REQUEST for group X, creating the VC,
sending the packet).
Assuming IPmcR.2 initialised itself with the MARS as described in section 6.2.3. This
requires it to register for a particular protocol (specified in the
ar$pro field member of the MARS_MSERV).
Each MCS MUST terminate unidirectional VCs in the same manner
entire Class D space, it will have been returned as a
cluster member would (e.g. terminate of X
even if no other nodes on an LLC entity when LLC/SNAP
encapsulation is used, as described in RFC 1755 the LIS were members. All packets for unicast
endpoints). This group
X received on IPmcR.2's LIS interface may be retransmitted on LAN.2.
If IPmcR.1 is because similarly initialised the MCS is acting as a surrogate cluster
endpoint reverse process will apply
for the senders multicast traffic from LAN.2 to the LAN.1, for any multicast group.
The MCS manages its outgoing point to multipoint VC in an analogous
way to a benefit of this scenario is that cluster member (as described members within the LIS
may also join and leave group X at anytime.
8.4 Joining in section 5.1). MARS_REQUEST
is used by 'semi-promiscuous' mode.
Both unicast and multicast IP routers have a common problem -
limitations on the MCS to establish number of AAL contexts available at their ATM
interfaces. Being 'promiscuous' in the initial leaf nodes RFC 1112 sense means that for the MCS's
outgoing point
every M hosts sending to multipoint VC. After the VC N groups, a multicast router's ATM interface
will have M*N incoming reassembly engines tied up.
It is established, not hard to envisage situations where a number of multicast
groups are active within the MCS
reacts LIS but are not required to MARS_SJOINs and MARS_SLEAVEs in be
propagated beyond the same way LIS itself. An example might be a cluster
member reacts distributed
simulation system specifically designed to MARS_JOINs and MARS_LEAVEs.
The MCS tracks the Server Sequence Number from use the ar$msn fields high speed IP/ATM
environment. There may be no practical way its traffic could be
utilised on 'the other side' of
messages from the MARS, and revalidates its outgoing point to
multipoint VC(s) when a sequence number jump occurs.
The MCS uses multicast router, yet under the same approach
conventional scheme the router would have to backup MARSs as be a cluster member,
and tracks MARS_REDIRECT_MAP messages on ServerControlVC in an
analogous manner leaf to cluster members (as described in section 5.4).
An MCS MUST NOT share each
participating host anyway.
As this problem occurs below the same ATM address as a cluster member,
although IP layer, it may share is worth noting that
'scoping' mechanisms at the same physical ATM interface.
8. Support for IP multicast routers.
Multicast routers are required for routing level do not provide
a solution. An IP level scope would still result in the propagation of multicast router's ATM
interface receiving traffic beyond on the constraints of a single cluster (inter-cluster
traffic). (There is a sense in which they are multicast servers
acting at scoped groups, only to drop it.
In this situation the next higher layer, with clusters, rather than
individual endpoints, as network administrator might configure their abstract sources and destinations.)
Multicast routers typically participate in higher layer
multicast
routing algorithms and policies that are beyond the scope routers to exclude sections of this
memo (e.g. DVMRP [5] in the IPv4 environment).
It is assumed Class D address space
when issuing MARS_JOIN(s). Multicast groups that the multicast routers will never be implemented over
propagated beyond the
same sort of IP/ATM interface that a multicast host would use. Their
IP/ATM interfaces will cluster will register with not have the MARS router listed as a cluster
members, joining
member, and leaving multicast groups as necessary. As noted
in section 5, multiple logical 'endpoints' may be implemented over the router will never have to receive (and simply ignore)
traffic from those groups.
Another scenario involves the product M*N exceeding the capacity of a
single physical ATM interface. Routers use this approach to provide
interfaces into each clusters they will be routing between. router's interface (especially if the same interface must also
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The rest
support a unicast IP router service).
A network administrator may choose to add a second node, to function
as a parallel IP multicast router. Each router would be configured to
be 'promiscuous' over separate parts of this section the Class D address space,
thus exposing themselves to only part of the VC load. This sharing
would be completely transparent to IP hosts within the LIS.
Restricted promiscuous mode does not break RFC 1112's use of IGMP
Report messages. If the router is configured to serve a given block
of Class D addresses, it will assume receive the IGMP Report. If the router
is not configured to support a given block, then the existence of an
IGMP Report for a group in that block is irrelevant to the router.
All routers are able to track membership changes through the
MARS_JOIN and MARS_LEAVE traffic anyway. (Section 8.5 discusses a simple IPv4 scenario where
better alternative to IGMP within a cluster.)
Mechanisms and reasons for establishing these modes of operation are
beyond the scope of a cluster has been limited this document.
8.5 An alternative to a particular LIS that IGMP Queries.
An unfortunate aspect of IGMP is part that it assumes multicasting of an overlaid IP network. Not all members of
packets is a cheap and trivial event at the LIS link layer. As a
consequence, regular IGMP Queries are necessarily
registered multicasted by routers to group
224.0.0.1. These queries are intended to trigger IGMP Replies by
cluster members (you may that have unicast-only hosts in the
LIS).
8.1 Forwarding layer 3 members of particular groups.
The MARS_GROUPLIST_REQUEST and MARS_GROUPLIST_REPLY messages were
designed to allow routers to avoid actually transmitting IGMP Queries
out into a Cluster.
If cluster.
Whenever the multicast router needs router's forwarding engine wishes to transmit an IGMP
query, a packet MARS_GROUPLIST_REQUEST can be sent to a group within the cluster its IP/ATM interface opens a VC MARS instead. The
resulting MARS_GROUPLIST_REPLY(s) (described in section 5.3) from the same manner as a
normal host would. Once a VC is open,
MARS carry all the information that the router watches for
MARS_JOIN and MARS_LEAVE messages and responds would have ascertained
from IGMP replies.
It is RECOMMENDED that multicast routers utilise this MARS service to them as
minimise IGMP traffic within the cluster.
By default a normal
host would.
The multicast router's transmit side MUST implement inactivity timers MARS_GROUPLIST_REQUEST SHOULD specify the entire address
space (e.g. <224.0.0.0, 239.255.255.255> in an IPv4 environment).
However, routers serving part of the address space (as described in
section 8.4) MAY choose to shut down idle outgoing VCs, as for normal hosts.
As with normal host, issue MARS_GROUPLIST_REQUESTs that specify
only the subset of the address space they are serving.
(On the surface it would also seem useful for multicast router does not need routers to
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track MARS_JOINs and MARS_LEAVEs that arrive with ar$flags.layer3grp
set. These might be a
member used in lieu of IGMP Reports, to provide the
router with timely indication that a new layer 3 group it is sending to.
8.2 Joining in 'promiscuous' mode.
Once registered and initialised, member exists
within the simplest model of IPv4 multicast
router operation cluster. However, this only works on VC mesh supported
groups, and is therefore NOT recommended).
Appendix B discusses less elegant mechanisms for it to issue a MARS_JOIN encompassing reducing the
entire Class D address space. In effect it becomes 'promiscuous', as
it will be impact
of IGMP traffic within a leaf node to all present and future multipoint VCs
established to IPv4 groups cluster, on the cluster.
How a router chooses which groups assumption that the IP/ATM
interfaces to propagate outside the cluster are being used by un-optimised IP
multicasting code.
8.6 CMIs across multiple interfaces.
The Cluster Member ID is
beyond only unique within the scope of Cluster managed by a
given MARS. On the surface this memo.
Consistent might appear to leave us with RFC 1112, IP a
problem when a multicast routers may retain the use of
IGMP Query and IGMP Report messages to ascertain group membership.
However, certain optimisations are possible, router is routing between two or more
Clusters using a single physical ATM interface. The router will
register with two or more MARSs, and are described thereby acquire two or more
independent CMI's. Given that each MARS has no reason to synchronise
their CMI allocations, it is possible for a host in
section 8.5.
8.3 Forwarding across one cluster to
have the cluster.
Under some circumstances same CMI has the cluster may simply be router's interface to another hop Cluster. How
does the router distinguish between IP subnets its own reflected packets, and
packets from that have participants other host?
The answer lies in the fact that routers (and hosts) actually
implement logical IP/ATM interfaces over a multicast group.
[LAN.1] ----- IPmcR.1 -- [cluster/LIS] -- IPmcR.2 ----- [LAN.2]
LAN.1 and LAN.2 are subnets (such as Ethernet) single physical ATM
interface. Each logical interface will have a unique ATM Address (eg.
an NSAP with attached hosts
that are members different SELector fields, one for each logical
interface).
Each logical IP/ATM interface is configured with the address of group X.
IPmcR.1 a
single MARS, attaches to only one cluster, and IPmcR.2 are multicast routers with interfaces so had only one CMI to
worry about. Each of the LIS.
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A traditional solution would be to treat MARSs that the LIS as router is registered with
will have been given a unicast subnet,
and use tunneling routers. However, this would not allow hosts on the
LIS different ATM Address (corresponding to participate the
different logical IP/ATM interfaces) in each registration MARS_JOIN.
When hosts in a cluster add the cross-LIS traffic.
Assume IPmcR.1 is receiving packets promiscuously on its LAN.1
interface. Assume further it is configured to propagate multicast
traffic to all attached interfaces. In this case that means router as a leaf node, they'll
specify the ATM Address of the LIS.
When a packet for group X arrives appropriate logical IP/ATM interface
on its LAN.1 interface, IPmcR.1
simply sends the packet to group X on router in the LIS L_MULTI_ADD message. Thus, each logical IP/ATM
interface as a normal
host would (Issuing MARS_REQUEST for group X, creating will only have to check and filter on CMIs assigned by its
own MARS.
In essence the VC,
sending cluster differentiation is achieved by ensuring that
logical IP/ATM interfaces are assigned different ATM Addresses.
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9. Multiprotocol applications of the packet).
Assuming IPmcR.2 initialised itself with MARS and MARS clients.
A deliberate attempt has been made to describe the MARS as and
associated mechanisms in a member manner independent of a specific higher
layer protocol being run over the
entire Class D space, it ATM cloud. The immediate
application of this document will have been returned as a member be in an IPv4 environment, and this
is reflected by the focus of X
even if no other nodes on key examples. However, the LIS were members. All packets for group
X received on IPmcR.2's LIS interface may coding of
each MARS message means that any higher layer protocol identifiable
by a two byte Ethernet Type code can be retransmitted on LAN.2.
If IPmcR.1 supported by a MARS.
As noted in section 4.3, the 16 bit 'Protocol type' (ar$pro) at the
start of each MARS message is similarly initialised taken from the reverse process will apply following two sets:
0x0000 to 0x05FF Reserved for multicast traffic future use by the IETF.
0x0600 to 0xFFFF Protocols defined by the matching Ethertypes.
Every MARS MUST implement entirely separate logical mapping tables
and support. Every cluster member must interpret messages from LAN.2 to LAN.1, for any multicast group.
The benefit the
MARS in the context of this scenario is the protocol type that cluster members within the LIS
may also join MARS message refers
to.
Every MARS and leave group X at anytime.
8.4 Joining MARS client MUST treat Cluster Member IDs in 'semi-promiscous' mode.
Both unicast and multicast IP routers have a common problem -
limitations on the number
context of AAL contexts available at their ATM
interfaces. Being 'promiscuous' the protocol type carried in the RFC 1112 sense means that for MARS message or data
packet containing the CMI.
For example, IPv6 has been allocated an Ethertype of 0x86DD. An IPv6
multicasting client sets the ar$pro field of every M hosts sending to N groups, a multicast router's ATM interface
will have M*N incoming reassembly engines tied up.
It is not hard MARS message to envisage situations where a number of multicast
groups are active within
0x86DD. When carrying IPv6 addresses the LIS but ar$spln and ar$tpln fields
are not required either 0 (for null or non-existent information) or 16 (for the
full IPv6 address).
The LLC/SNAP encapsulations described in section 5 similarly allow
multiple protocols to be
propagated beyond identified by the LIS itself. An example might be a distributed
simulation system specifically designed to use of different values in
appropriate encapsulation fields.
For example, an IPv6 packet is encapsulated as:
[0xAA-AA-03][0x00-00-5E][0x00-01][pkt$cmi][0x86DD][IPv6 packet]
A host or endpoint interface that is using the high speed IP/ATM
environment. There may same MARS to support
multicasting needs of multiple protocols MUST not assume their CMI
will be no practical way its traffic could the same for each protocol.
Values for ar$pro in the range 0 to 0x5FF may be
utilised assigned specific
interpretations by the IETF in future documents.
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10. Supplementary parameter processing.
MARS messages currently have a common header, followed by a variable
set of fields whose interpretation depends on 'the other side' the contents of the multicast router, yet under
ar$op field. The format of these fields, and their contents, reflect
the
conventional scheme minimum information currently deemed necessary to support the router would
MARS model.
Every MARS message carries an ar$extoff field, immediately following
the ar$op field. Its role is to indicate whether supplementary
parameters have been supplied along with the basic address mappings.
(This mechanism will enable the addition of additional functionality
to be the MARS protocol in later documents.)
Supplementary parameters are conveyed as a leaf to each
participating host anyway.
As this problem occurs at list of TLV (type, length,
value) encoded information elements. The TLV(s) begin on the link layer, it is worth noting that
'scoping' mechanisms at first
32 bit boundary following the IP multicast routing level do not provide
a solution. An IP level scope would still result last 'conventional' field in the router's ATM
interface receiving traffic on MARS
message (e.g. after ar$tsa.N in a MARS_MULTI, after ar$max.N in a
MARS_JOIN, etc).
10.1 Interpreting the scoped groups, only to drop it.
In this situation ar$extoff field.
If the network administrator might configure their
multicast routers to exclude sections bottom 16 bits of the Class D address space
when issuing MARS_JOIN(s). Multicast groups ar$extoff field are non-zero it
indicates that will never be
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propagated beyond the cluster will not a list of one or more TLVs have been appended to the
MARS message. The bottom 16 bits of ar$extoff then represent an
unsigned integer an offset (in octets) from the router listed as a
member, and beginning of the router will never have MARS
message (the MSB of the ar$hrd field) to receive (and simply ignore)
traffic from those groups.
Another scenario involves the product M*N exceeding first TLV.
As TLVs are 32 bit aligned the capacity bottom 2 bits of a
single router's interface (especially if the same interface must ar$extoff are also
support a unicast IP router service).
reserved. A network administrator may choose to add a second node, receiver MUST mask off these two bits before calculating
the octet offset to function
as a parallel IP multicast router. Each router would be configured the TLV list. A sender MUST set these two bits
to
be 'promiscuous' over separate parts of zero.
If the Class D address space,
thus exposing themselves bottom 16 bits of ar$extoff are zero no TLVs have been
appended to only part the basic MARS message.
The top 16 bits of ar$extoff (the two bytes immediately following the VC load. This sharing
would be completely transparent to
ar$op field) carry a standard IP hosts within checksum calculated across the LIS.
Restricted promiscuous mode
entire MARS message (which does not break RFC 1112's use of IGMP
Report messages. If include the router is configured LLC/SNAP header).
These 16 bits are set to serve a given block
of Class D addresses, it will receive the IGMP Report. If zero before performing the router
is not configured calculation prior
to support a given block, then the existence transmission of an
IGMP Report for a group in that block message.
As the entire LLC/SNAP encapsulated MARS message is irrelevant protected by the
32 bit CRC of the AAL5 transport, implementors MAY choose to ignore
the router.
All routers checksum facility. If no checksum is calculated these bits MUST
be reset before transmission.
Implementations that do not implement checksumming MUST silently
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discard messages received with these bits non-zero. Otherwise, if
these bits are able to track membership changes through non-zero on reception the
MARS_JOIN and MARS_LEAVE traffic anyway. (Section 8.5 discusses a
better alternative to IGMP within receiver MUST perform a cluster.)
Mechanisms
checksum computation and reasons for establishing these modes of operation discard the packet silently if the checksums
do not match. The checksum bits are
beyond treated as zero for the scope purpose
of the receive side checksum calculation.
Checksum generation and processing are NOT REQUIRED for conformance
with this memo.
8.5 An alternative to IGMP Queries.
An unfortunate aspect document.
10.2 The format of IGMP is that it assumes multicasting TLVs.
When they exist, TLVs begin on 32 bit boundaries, are multiples of IP
packets is a cheap 32
bits in length, and trivial event at the link layer. As form a
consequence, regular IGMP Queries are multicasted sequential list terminated by routers to group
224.0.0.1. These queries a NULL TLV.
The TLV structure is:
[Type - 2 octets][Length - 2 octets][Value - n*4 octets]
The Type subfield indicates how the contents of the Value subfield
are intended to trigger IGMP Replies by
cluster members that have layer 3 members be interpreted.
The Length subfield indicates the number of particular groups.
However, VALID octets in the MARS_GROUPLIST_REQUEST and MARS_GROUPLIST_REPLY messages
were designed Value
subfield. Valid octets in the Value subfield start immediately after
the Length subfield. ((Length & 0xFFF7) + 4) provides the offset (in
octets) to allow routers the start of the next TLV in the list.
The Value subfield is padded with 0, 1, 2, or 3 octets to avoid actually transmitting IGMP
Queries out into a cluster.
Whenever ensure the router's forwarding engine wishes
next TLV is 32 bit aligned. The padded locations MUST be set to transmit an IGMP
query, zero.
(For example, a MARS_GROUPLIST_REQUEST can TLV that needed only 5 valid octets of information
would be 12 octets long. The Length subfield would hold the value 5,
and the Value subfield would be sent padded out to 8 bytes. The 5 valid
octets of information begin at the MARS instead. first octet of the Value
subfield.)
The
resulting MARS_GROUPLIST_REPLY(s) (described Type subfield is formatted in section 5.3) from the
MARS carry all following way:
| 1st octet | 2nd octet |
7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| x | y |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The most significant 2 bits (Type.x) determine how a recipient should
behave when it doesn't recognise the information that TLV type indicated by the router would have ascertained
from IGMP replies.
It is RECOMMENDED that multicast routers utilise this MARS service to
minimise IGMP traffic within lower
14 bits (Type.y). The required behaviours are:
Type.x = 0 Skip the cluster.
By default a MARS_GROUPLIST_REQUEST SHOULD specify TLV, continue processing the entire address list.
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space (e.g. <224.0.0.0, 239.255.255.255> in an IPv4 environment).
However, routers serving part of
Type.x = 1 Stop processing, silently drop the address space (as described MARS message.
Type.x = 2 Stop processing, drop message, give error indication.
Type.x = 3 Reserved. (currently treat as x = 0)
(The error indication generated when Type.x = 2 SHOULD be logged in
section 8.4) MAY choose to issue MARS_GROUPLIST_REQUESTs that specify
only the subset of the address space they are serving.
(On the surface it would also seem useful for multicast routers
some locally significant fashion. Consequential MARS message activity
in response to
track MARS_JOINs and MARS_LEAVEs that arrive with the ar$layer3grp
flag set. These might such an error condition will be used defined in lieu of IGMP Reports, to provide the
router with timely indication that a new layer 3 group member exists
within the cluster. However, this only works on VC mesh supported
groups, and future
documents.)
The TLV type space (Type.y) is therefore NOT recommended).
Appendix B discusses less elegant mechanisms further subdivided to encourage use
outside the IETF.
0 Null TLV.
0x0001 - 0x0FFF Reserved for reducing the impact
of IGMP traffic within a cluster, on IETF.
0x1000 - 0x11FF Allocated to the assumption that ATM Forum.
0x1200 - 0x37FF Reserved for the IP/ATM
interfaces IETF.
0x3800 - 0x3FFF Experimental use.
10.3 Processing MARS messages with TLVs.
Supplementary parameters act as modifiers to the cluster are being used basic behaviour
specified by un-optimised IP
multicasting code.
9. Multiprotocol applications of the ar$op field of any given MARS and message.
If a MARS clients.
A deliberate attempt has been made to describe message arrives with a non-zero ar$extoff field its TLV
list MUST be parsed before handling the MARS and
associated mechanisms message in a manner independent of a specific higher
layer protocol being run over accordance
with the ATM cloud. The immediate
application of this document ar$op value. Unrecognised TLVs must be handled as required
by their Type.x value.
How TLVs modify basic MARS operations will be in an IPv4 environment, ar$op and TLV specific.
10.4 Initial set of TLV elements.
Conformance with this
is reflected by document only REQUIRES the focus recognition of key examples. However, one
TLV, the coding of
each MARS message means that any higher layer protocol identifiable
by Null TLV. This terminates a two byte Ethernet Type code can list of TLVs, and MUST be supported by
present if ar$extoff is non-zero in a MARS.
The 16 bit 'Protocol type' (ar$pro) at the start of each MARS message message. It MAY be the
only TLV present.
It is taken from coded simply as:
[0x00-00][0x00-00]
Future documents will describe the set of Ethernet Type codes. Every MARS MUST
implement entirely separate logical mapping tables formats, contents, and support. Every
cluster member must interpret messages from the MARS in the context
interpretations of the protocol type that the MARS message refers to. additional TLVs. The LLC/SNAP encapsulations described in section 5 similarly minimal parsing requirements
imposed by this document are intended to allow
multiple protocols conformant MARS and
MARS client implementations to be identified by the use of different values in
appropriate encapsulation fields.
10. deal gracefully and predictably with
future TLV developments.
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11. Key Decisions and open issues.
The key decisions this memo document proposes:
A Multicast Address Resolution Server (MARS) is proposed to co-
ordinate and distribute mappings of ATM endpoint addresses to
arbitrary higher layer 'multicast group addresses'. The specific
case of IPv4 multicast is used as the example.
The concept of 'clusters' is introduced to define the scope of a
MARS's responsibility, and the set of ATM endpoints willing to
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participate in link level multicasting.
A Class I MARS is described, with the necessary functionality to
support intra-cluster multicasting using VC meshes. A Class II MARS is described as a superset of the Class I, with additional the functionality required to support
intra-cluster multicasting using either VC meshes or ATM level
multicast servers. servers (MCSs).
MARS message formats and encapsulation allow co-resident MARS and
ATM ARP Server implementations.
New message types:
MARS_JOIN, MARS_LEAVE, MARS_REQUEST. Allow endpoints to join,
leave, and request the current membership list of multicast
groups.
New message type:
MARS_MULTI. Allows multiple ATM addresses to be returned by the
MARS in response to a MARS_REQUEST.
New message types:
MARS_MSERV, MARS_UNSERV. Allow multicast servers to register
and deregister themselves with the MARS.
New message types:
MARS_SJOIN, MARS_SLEAVE. Allow MARS to pass on group membership
changes to multicast servers.
New message types:
MARS_GROUPLIST_REQUEST, MARS_GROUPLIST_REPLY. Allow MARS to
indicate which groups have actual layer 3 members. May be used
to support IGMP in IPv4 environments, and similar functions in
other environments.
New message type:
MARS_REDIRECT_MAP. Allow MARS to specify a set of backup MARS
addresses.
'wild card' MARS mapping table entries possible, where a single
ATM address is simultaneously associated with blocks of multicast
group addresses.
The complete set of messages, and ar$op values, is:
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11 MARS_REQUEST
12 MARS_MULTI
13 MARS_MSERV
14 MARS_JOIN
15 MARS_LEAVE
16 MARS_NAK
17 MARS_UNSERV
18 MARS_SJOIN
19 MARS_SLEAVE
20 MARS_GROUPLIST_REQUEST
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21 MARS_GROUPLIST_REPLY
22 MARS_REDIRECT_MAP
A number of issues are left open at this stage, and are likely to be
the subject of on-going research and additional documents that build
upon this one.
The specified endpoint behaviour allows the use of
redundant/backup MARSs within a cluster. However, no
specifications yet exist on how these MARSs co-ordinate amongst
themselves. (The default is to only have one MARS per cluster.)
The specified endpoint behaviour and Class II MARS service allows the use
of multiple MCSs per group. However, no specifications yet exist
on how this may be used, or how these MCSs co-ordinate amongst
themselves. (The Until futher work is done on MCS co-ordination
protocols the default is to only have one MCS per
group.) group.
The MARS relies on the cluster member dropping off
ClusterControlVC if the cluster member dies. It is not clear if
additional mechanisms are needed to detect and delete 'dead'
cluster members.
If a multicast server attempts to MARS_MSERV for an existing VC
mesh supported group, it would be nice to have current senders to
the group migrate their outgoing VCs from the actual cluster
member leaf nodes to the newly registered multicast server(s). How
this might be achieved, the load this would place on the MARS, and
its scalability, have not yet been considered.
Supporting layer 3 'broadcast' as a special case of multicasting
(where the 'group' encompasses all cluster members) has not been
explicitly discussed.
Supporting layer 3 'unicast' as a special case of multicasting
(where the 'group' is a single cluster member, identified by the
cluster member's unicast protocol address) has not been explicitly
discussed.
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The future development of ATM Group Addresses and Leaf Initiated
Join to ATM Forum's UNI specification has not been addressed.
(However, the problems identified in this memo document with respect to
VC scarcity and impact on AAL contexts will not be fixed by such
developments in the signalling protocol.)
Security Consideration
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Security consideration are not addressed in this memo. document.
Acknowledgments
The discussions within the IP over ATM Working Group have helped
clarify the ideas expressed in this document. John Moy (Cascade
Communications Corp.) initially suggested the idea of wild-card
entries in the ARP Server. Drew Perkins (Fore Systems) provided
rigorous and useful critique of early proposed mechanisms for
distributing and validating group membership information. Susan
Symington (and co-workers at MITRE Corp., Don Chirieleison, Rich
Verjinski, and Bill Barns) clearly articulated the need for multicast
server support, proposed a solution, and challenged earlier block
join/leave mechanisms. John Shirron (Fore Systems) provided useful
improvements on my original revalidation procedures. Susan Symington
and Bryan Gleeson (Adaptec) independently championed the need for the
service provided by MARS_GROUPLIST_REQUEST/REPLY. The new
encapsulation scheme arose from WG discussions, captured by Bryan
Gleeson in an interim Internet Draft (with Keith McCloghrie (Cisco),
Andy Malis (Ascom Nexion), and Andrew Smith (Bay Networks) as key
contributors).
Author's Address
Grenville Armitage
MRE 2P340, 2P255, 445 South Street
Morristown, NJ, 07960
USA
Email: gja@thumper.bellcore.com
Ph. +1 201 829 2635
References
[1] S. Deering, "Host Extensions for IP Multicasting", RFC 1112,
Standford University, August 1989.
[2] Heinanen, J., "Multiprotocol Encapsulation over ATM Adaption
Layer 5", RFC 1483, USC/Information Science Institute, July 1993.
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[3] Laubach, M., "Classical IP and ARP over ATM", RFC1577, Hewlett-
Packard Laboratories, December 1993
[4] ATM Forum, "ATM User-Network User Network Interface (UNI) Specification
Version
3.0", Englewood Cliffs, NJ: 3.1", ISBN 0-13-393828-X, Prentice Hall, September 1993 Englewood Cliffs,
NJ, June 1995.
[5] D. Waitzman, C. Partridge, S. Deering, "Distance Vector Multicast
Routing Protocol", RFC 1075, November 1988.
[6] M. Perez, F. Liaw, D. Grossman, A. Mankin, E. Hoffman, A. Malis,
"ATM Signaling Support for IP over ATM", RFC 1755, February 1995.
[7] M. Borden, E. Crawley, B. Davie, S. Batsell, "Integration of
Real-time Services in an IP-ATM Network Architecture.", RFC 1821,
August 1995.
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Appendix A. Hole punching algorithms for Class II MARS messages. algorithms.
Implementations are entirely free to comply with the body of this
memo in any way they see fit. This appendix is purely for
clarification.
A Class II MARS implementation might pre-construct a set of <min,max> pairs
(P) that reflects the entire Class D space, excluding any addresses
currently supported by multicast servers. The <min> field of the
first pair MUST be 224.0.0.0, and the <max> field of the last pair
must be 239.255.255.255. The first and last pair may be the same.
This set is updated whenever a multicast server registers or
deregisters.
When the MARS must perform 'hole punching' it might consider the
following algorithm:
Assume the MARS_JOIN/LEAVE received by the MARS from the cluster
member specied the block <Emin, Emax>.
Assume Pmin(N) and Pmax(N) are the <min> and <max> fields from the
Nth pair in the MARS's current set P.
Assume set P has K pairs. Pmin(1) MUST equal 224.0.0.0, and
Pmax(M) MUST equal 239.255.255.255. (If K == 1 then no hole
punching is required).
Execute pseudo-code:
create copy of set P, call it set C.
index1 = 1;
while (Pmax(index1) <= Emin)
index1++;
index2 = K;
while (Pmin(index2) >= Emax)
index2--;
if (index1 > index2)
Exit, as the hole-punched set is null.
if (Pmin(index1) < Emin)
Cmin(index1) = Emin;
if (Pmax(index2) > Emax)
Cmax(index2) = Emax;
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Set C is the required 'hole punched' set of address blocks.
The resulting set C retains all the MARS's pre-constructed 'holes'
covering the multicast servers, but will have been pruned to cover
the section of the Class D space specified by the originating host's
<Emin,Emax> values.
The host end should keep a table, H, of open VCs in ascending order
of Class D address.
Assume H(x).addr is the Class address associated with VC.x.
Assume H(x).addr < H(x+1).addr.
The pseudo code for updating VCs based on an incoming JOIN/LEAVE
might be:
x = 1;
N = 1;
while (x < no.of VCs open)
{
while (H(x).addr > max(N))
{
N++;
if (N > no. of pairs in JOIN/LEAVE)
return(0);
}
if ((H(x).addr <= max(N) &&
((H(x).addr >= min(N))
perform_VC_update();
x++;
}
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Appendix B. Minimising the impact of IGMP in IPv4 environments.
Implementing any part of this appendix is not required for
conformance with this memo. document. It is provided solely to document
issues that have been identified.
The intent of section 5.1 is for cluster members to only have
outgoing point to multipoint VCs when they are actually sending data
to a particular multicast groups. However, in most IPv4 environments
the multicast routers attached to a cluster will periodically issue
IGMP Queries to ascertain if particular groups have members. The
current IGMP specification attempts to avoid having every group
member respond by insisting that each group member wait a random
period, and responding if no other member has responded before them.
The IGMP reply is sent to the multicast address of the group being
queried.
Unfortunately, as it stands the IGMP algorithm will be a nuisance for
cluster members that are essentially passive receivers within a given
multicast group. It is just as likely that a passive member, with no
outgoing VC already established to the group, will decide to send an
IGMP reply - causing a VC to be established were there was no need
for one. This is not a fatal problem for small clusters, but will
seriously impact on the ability of a cluster to scale.
The most obvious solution is for routers to use the
MARS_GROUPLIST_REQUEST and MARS_GROUPLIST_REPLY messages, as
described in section 8.5. This would remove the regular IGMP Queries,
resulting in cluster members only sending an IGMP Report when they
first join a group.
Alternative solutions do exist. One would be to modify the IGMP reply
algorithm, for example:
If the group member has VC open to the group proceed as per RFC
1112 (picking a random reply delay between 0 and 10 seconds).
If the group member does not have VC already open to the group,
pick random reply delay between 10 and 20 seconds instead, and
then proceed as per RFC 1112.
If even one group member is sending to the group at the time the IGMP
Query is issued then all the passive receivers will find the IGMP
Reply has been transmitted before their delay expires, so no new VC
is required. If all group members are passive at the time of the IGMP
Query then a response will eventually arrive, but 10 seconds later
than under conventional circumstances.
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The preceeding solution requires re-writing existing IGMP code, and
implies the ability of the IGMP entity to ascertain the status of VCs
on the underlying ATM interface. This is not likely to be available
in the short term.
One short term solution is to provide something like the preceeding
functionality with a 'hack' at the IP/ATM driver level within cluster
members. Arrange for the IP/ATM driver to snoop inside IP packets
looking for IGMP traffic. If an IGMP packet is accepted for
transmission, the IP/ATM driver can buffer it locally if there is no
VC already active to that group. A 10 second timer is started, and if
an IGMP Reply for that group is received from elsewhere on the
cluster the timer is reset. If the timer expires, the IP/ATM driver
then establishes a VC to the group as it would for a normal IP
multicast packet.
Some network implementors may find it advantageous to configure a
multicast server to support the group 224.0.0.1, rather than rely on
a mesh. Given that IP multicast routers regularly send IGMP queries
to this address, a mesh will mean that each router will permanently
consume an AAL context within each cluster member. In clusters served
by multiple routers the VC load within switches in the underlying ATM
network will become a scaling problem.
Finally, if a multicast server is used to support 224.0.0.1, another
ATM driver level hack becomes a possible solution to IGMP Reply
traffic. The ATM driver may choose to grab all outgoing IGMP packets
and send them out on the VC established for sending to 224.0.0.1,
regardless of the Class D address the IGMP message was actually for.
Given that all hosts and routers must be members of 224.0.0.1, the
intended recipients will still receive the IGMP Replies. The negative
impact is that all cluster members will receive the IGMP Replies.
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Appendix C. Further comments on 'Clusters'.
The cluster concept was introduced in section 1 for two reasons. The
more well known term of Logical IP Subnet is both very IP specific,
and constrained to unicast routing boundaries. As the architecture
described in this document may be re-used in non-IP environments a
more neutral term was needed. As the needs of multicasting are not
always bound by the same scopes as unicasting, it was not immediately
obvious that apriori limiting ourselves to LISs was a win situation
either. beneficial in the
long term.
It must be stressed that Clusters are purely an administrative being.
You choose their size (i.e. the number of endpoints that register
with the same MARS) based on your multicasting needs, and the
resource consumption you are willing to put up with. The larger the
number of ATM attached hosts you require multicast support for, the
more individual clusters you may might choose to establish (along with
multicast routers to provide inter-cluster traffic paths).
Given that not all the hosts in any given LIS may require multicast
support, it becomes conceivable that you might assign a single MARS
to support hosts from across multiple LISs. In effect you have a
cluster covering multiple LISs, and have achieved 'cut through'
routing for multicast traffic. Under these circumstances increasing
the geographical size of a cluster might be considered a good thing.
However, practical considerations limit the size of clusters. Having
a cluster span multiple LISs may not always be a particular 'win'
situation. As the number of multicast capable hosts in your LISs
increases it becomes more likely that you'll want to constrain a
cluster's size and force multicast traffic to aggregate at multicast
routers scattered across your ATM cloud. (This is especially true
for clusters based on Class I MARSs, as resource consumption of VC
meshes increases rapidly with an increase in the number of
senders/group members.) to aggregate at multicast
routers scattered across your ATM cloud.
Finally, multi-LIS clusters require a moderate amount degree of care when deploying
IP multicast routers. Under the Classical IP model you need unicast
routers on the edges of LISs. Under the MARS architecture you only
need multicast routers at the edges of clusters. If your cluster
spans multiple LISs, then the multicast routers will perceive
themselves to have a single interface that is simultaneously attached
to multiple unicast subnets. This Whether this situation can work, but may require
some hand configuration of 'default' multicast router behaviour,
depending will work depends
on the inter-domain multicast routing protocol protocols you are using. use, and your
multicast router's ability to understand the new relationship between
unicast and multicast topologies.
In the absence of futher research in this area, networks deployed in
conformance to this document MUST make their IP cluster and IP LIS
coincide, so as to avoid these complications.
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Appendix D. TLV list parsing algorithm.
The following pseudo-code represents how the TLV list format
described in section 10 could be handled by a MARS or MARS client.
list = (ar$extoff & 0xFFF7);
if (list == 0) exit;
list = list + message_base;
while (list->Type.y != 0)
{
switch (list->Type.y)
{
default:
{
if (list->Type.x == 0) break;
if (list->Type.x == 1) exit;
if (list->Type.x == 2) log-error-and-exit;
}
[...other handling goes here..]
}
list += ((list->Length & 0xFFF7) + 4);
}
return;
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Internet Draft <draft-ietf-ipatm-ipmc-06.txt> August 11th, 1995
Appendix E. Summary of timer values.
This appendix summarises of various timers or limits mentioned in the
main body of the document. Values are specified in the following
format: [x, y, z] indicating a minimum value of x, a recommended
value of y, and a maximum value of z. A '-' will indicate that a
category has no value specified. Values in minutes are followed by
'min', values in seconds are followed by 'sec'.
Idle time for MARS - MARS client pt to pt VC:
[1 min, 20 min, -]
Idle time for multipoint VCs from client.
[1 min, 20 min, -]
Allowed time between MARS_MULTI components.
[-, -, 10 sec]
Initial random L_MULTI_RQ/ADD retransmit timer range.
[5 sec, -, 10 sec]
Random time to set VC_revalidate flag.
[1 sec, -, 10 sec]
MARS_JOIN/LEAVE retransmit interval.
[5 sec, 10 sec, -]
MARS_JOIN/LEAVE retransmit limit.
[-, -, 5]
Random time to re-register with MARS.
[1 sec, -, 10 sec]
Force wait if MARS re-registration is looping.
[1 min, -, -]
Transmission interval for MARS_REDIRECT_MAP.
[1 min, 1 min, 2 min]
Limit for client to miss MARS_REDIRECT_MAPs.
[-, -, 4 min]
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