WDIFF

draft-pmohapat-idr-info-safi-01.txt --> draft-pmohapat-idr-info-safi-02.txt

Network Working Group Pradosh Mohapatra
Internet Draft Cisco Systems, Inc.
Expiration Date: August December 2007
Eric Rosen
Cisco Systems, Inc.

February

June 2007

BGP Encapsulation SAFI and BGP Tunnel Encapsulation Attribute

draft-pmohapat-idr-info-safi-01.txt

draft-pmohapat-idr-info-safi-02.txt

Status of this Memo

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Abstract

This document specifies

In certain situations, transporting a new BGP SAFI, Encapsulation SAFI. A packet from one BGP
update message of this SAFI contains an NLRI which uniquely
identifies speaker to
another, the BGP speaker next hop, requires that originated the update. The purpose of
such an update is to carry attributes that define how encapsulated
packets need to packet be delivered to encapsulated
by the sender. For instance, if one first BGP speaker and decapsulated by the second. To support
these situations, there needs to use an IP-based encapsulation in order to deliver
traffic to a second, be some agreement between the second two
BGP speaker can use this SAFI speakers with regard to
specify information about the "encapsulation information", i.e.,
the format of the encapsulation header that it expects. A
BGP tunnel as well as the contents of
various fields of the header.

The encapsulation attribute is specified information need not be signaled for this purpose. all

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Other attributes, including communities and/or

encapsulation types. In the cases where the signaling is required
(such as L2TPv3, GRE with key), This draft specifies a method by
which BGP speakers can signal encapsulation information to each
other. The signaling is done by sending BGP updates using the
"Encapsulation SAFI" and IPv4 or IPv6 AFI. In the cases where no
encapsulation information needs to be signaled (such as GRE without
key), this draft specifies a BGP extended communities, community that can also be included.
attached to UPDATE messages that carry payload prefixes to indicate
the encapsulation protocol type to be used.

Table of Contents

1 Specification of requirements ...................... 2
2 Introduction ....................................... 2 3
3 Encapsulation NLRI Format .......................... 3 4
4 Tunnel Encapsulation Attribute ..................... 4 5
4.1 Encapsulation sub-TLV .............................. 6 7
4.2 Protocol Type sub-TLV .............................. 7 8
4.3 Tunnel Type Selection .............................. 7 9
4.4 BGP Encapsulation Extended Community ............... 9
5 Capability advertisement ........................... 8 10
6 Security Considerations ............................ 8 10
7 IANA Considerations ................................ 8 10
8 Acknowledgements ................................... 9 11
9 Normative References ............................... 9 11
10 Informative References ............................. 9 11
11 Authors' Addresses ................................. 9 11
12 Full Copyright Statement ........................... 10 12
13 Intellectual Property .............................. 10 12

1. Specification of requirements

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].

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2. Introduction

This document specifies a new BGP SAFI, Encapsulation SAFI. A BGP
update message

Consider the case of this SAFI contains a router R1 forwarding an NLRI which uniquely
identifies the BGP speaker IP packet P. Let D be
P's IP destination address. R1 must look up D in its forwarding
table. Suppose that originated the update. The purpose of
such "best match" route for D is route Q, where Q
is a BGP-distributed route whose "BGP next hop" is router R2. And
suppose further that the routers along the path from R1 to R2 have
entries for R2 in their forwarding tables, but do NOT have entries
for D in their forwarding tables. For example, the path from R1 to R2
may be part of a "BGP-free core", where there are no BGP-distributed
routes at all in the core. Or, as in [Softwires-Mesh-Frame-work], D
may be an update IPv4 address while the intermediate routers along the path
from R1 to R2 may support only IPv6.

In cases such as this, in order for R1 to properly forward packet P,
it must encapsulate P, and send P "through a tunnel" to R2. For
example, R1 may encapsulate P using GRE, L2TPv3, IP-in-IP, etc.,
where the destination IP address of the encapsulation header is the
address of R2.

In order for R1 to carry attributes that define how encapsulated encapsulate P for transport to R2, R1 must know
what encapsulation protocol to use for transporting what sorts of
packets need to be delivered R2. R1 must also know how to fill in the sender. For instance, if one various fields of
the encapsulation header. With certain encapsulation types, this
knowledge may be acquired by default or through manual configuration.
Other encapsulation protocols have fields such as session id, key, or
cookie which must be filled in. It would not be desirable to require
every BGP speaker needs to use an IP-based be manually configured with the encapsulation
information for every one of its BGP next hops.

In this draft, we specify a way in order which BGP itself can be used by a
given BGP speaker to deliver
traffic tell other BGP speakers, "if you need to a second,
encapsulate packets to be sent to me, here's the second information you need
to properly form the encapsulation header". A BGP speaker can use signals
this information to other BGP speakers by using a distinguished SAFI
value, the Encapsulation SAFI. The encapsulation SAFI can be used
with the AFI for IPv4 or with the AFI for IPv6. The IPv4 AFI is used
when the encapsulated packets are to
specify information about be sent using IPv4; the IPv6 AFI
is used when the encapsulated packets are to be sent using IPv6.

In a given BGP update, the NLRI of the encapsulation header SAFI consists of
the IP address (in the family specified by the AFI) of the originator
of that it expects. A
BGP tunnel update. The encapsulation attribute information is specified for this purpose. in one or
more BGP "tunnel encapsulation attributes" (specified herein). These
attributes specify the encapsulation protocols that may be used, as
well as specifying whatever additional information (if any) is needed
in order to properly use those protocols. Other attributes, including e.g.,
communities and/or or extended communities, may also be included.

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can also be included. The tunnel attribute is especially useful for
multipoint-to-point tunnels to signal information from

Since the receiving
speaker to transmitting speakers.

One application encapsulation information is coded as a set of the attributes,
one could ask whether a new SAFI and is really required. After all, a
BGP speaker could simply attach the tunnel encapsulation attribute is
[SOFTWIRE] that specifies a requirement attributes
to connect IPv4 networks
across IPv6 core and IPv6 networks across IPv4 core.

The motivation behind introducing each prefix (like Q in our example) that it advertises. But with
that technique, any change in the new SAFI to send encapsulation information
about the speaker is would
cause a very large number of updates. Unless one really wants to advertise such
specify different encapsulation information once, or as and
when for each prefix, it changes as opposed is
much better to attaching this information with each
and every prefix. That would require advertising redundant
information, and also, when have a mechanism in which a change in the
encapsulation information changes, the causes a BGP speaker
would require to send all the prefixes again resulting in advertise only a network-
wide control plane churn.

The advantage of using
single update. Conversely, when prefixes get modified, the same SAFI to distribute tunnel
encapsulation information of different tunneling technologies is that the route
reflectors need not be upgraded each time there exchanged.

In this specification, a single SAFI is used to carry information for
all encapsulation protocols. One could have taken an alternative
approach of defining a new SAFI for each encapsulation protocol deployed in protocol.
However, with the network specified approach, encapsulation information can
pass transparently and also automatically through intermediate BGP
speakers (e.g., route reflectors) that do not necessarily understand
the edge
routers can send or receive encapsulation parameters for multiple
types over one BGP session. The tunnel information. This works because the encapsulation
attribute is defined as an optional transitive, transitive attribute. New
encapsulations can thus a be added without the need to reconfigure any
intermediate BGP speaker can transparently pass on system. If adding a new encapsulation required using
a new SAFI, the information even if it does for that encapsulation would not pass
through intermediate BGP systems unless those systems were
reconfigured to support it. the new SAFI.

For encapsulation protocols where no encapsulation information needs
to be signaled (such as GRE without key), the egress router MAY still
want to specify the protocol to use for transporting packets from the
ingress router. This draft specifies a new BGP extended community
that can be attached to UPDATE messages that carry payload prefixes
for this purpose.

3. Encapsulation NLRI Format

The BGP speaker identification NLRI, defined below, is advertised carried in BGP UPDATE messages [RFC4271]
using MP_REACH_NLRI BGP multiprotocol extensions [RFC4760] with an AFI of 1 or 2
(IPv4 or IPv6) [IANA-AF] and MP_UNREACH_NLRI attributes [RFC4760]. The
Encapsulation a SAFI (value value to be assigned by IANA) is set as the SAFI
value in these UPDATE messages. The AFI is set to be one of the
address family identifier values IANA
(called as defined in [IANA-AF] (refer to
the Address Family Numbers section). Encapsulation SAFI).

The NLRI in the MP_REACH_NLRI or MP_UNREACH_NLRI is a variable length
field encoded in a format as defined in section 5 of [RFC4760]
(a 2-
tuple 2-tuple of the form <length, value>). The value field is
structured as follows:

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+-----------------------------------------------+
| Endpoint address (Variable) |
+-----------------------------------------------+

- Endpoint Address: This field identifies the BGP speaker
originating the update. It is typically one of the interface
addresses configured at the router. The length of the endpoint
address is dependent on the AFI being advertised. For example, if If the AFI is
set to IPv4 (1), the the endpoint address is a 4-octet IPv4
address whereas if the AFI is set to IPv6 (2), the endpoint
address is a 16-octet IPv6 address.

An update message that carries the MP_REACH_NLRI or MP_UNREACH_NLRI
with Encapsulation SAFI MUST also carry the BGP mandatory attributes:
ORIGIN, AS_PATH, and LOCAL_PREF (for IBGP neighbors) as defined in
[RFC4271]. In addition, such an update message can also contain any
of the BGP optional attributes, like Community or Extended Community
attribute to influence an action on the receiving speaker.

When a BGP speaker advertises the Encapsulation NLRI via BGP, it uses
its own address as the BGP nexthop in the MP_REACH_NLRI or
MP_UNREACH_NLRI attribute. The nexthop address is set based on the
AFI in the attribute. For example, if the AFI is set to IPv4 (1),
the nexthop is encoded as a 4-byte IPv4 address. If the AFI is set to
IPv6 (2), the nexthop is encoded as a 16-byte IPv6 address of the
router. On the receiving router, the BGP nexthop of such an update
message is validated by performing a recursive route lookup operation
in the routing table.

Bestpath selection of Encapsulation NLRIs is governed by the decision
process outlined in section 9.1 of [RFC4271]. The encapsulation data
carried through other attributes in the message are to be used by the
receiving router only if the NLRI has a bestpath.

4. Tunnel Encapsulation Attribute

Tunnel Encapsulation attribute is an optional transitive attribute
that is composed of a set of TLVs. The type code of the attribute is
to be assigned by IANA. Each TLV contains information corresponding
to a particular tunnel technology. The TLV is structured as follows:

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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tunnel Type (2 Octets) | Length (2 Octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Value |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Tunnel Type (2 octets): It identifies the type of the tunneling
technology being signaled. This document defines the following types:

- L2TPv3: Tunnel Type = 1

- GRE: Tunnel Type = 2

Unknown types are to be ignored and skipped upon receipt.

Length (2 octets): the total number of octets of the Value field.

Value (variable): The value is comprised of multiple sub-TLV's. Each
sub-TLV consists of three fields: a one-octet type, one-octet length,
and zero or more octets of value. The sub-TLV is structured as
follows:

+-----------------------------------+
| Sub-TLV Type (1 Octet) |
+-----------------------------------+
| Sub-TLV Length (1 Octet) |
+-----------------------------------+
| Sub-TLV Value (Variable) |
| |
+-----------------------------------+

Sub-TLV Type (1 octet): Each sub-TLV type defines a certain property
about the tunnel TLV that contains this sub-TLV. The following are
the types defined in this document:

- Encapsulation: sub-TLV type = 1

- Protocol type: sub-TLV type = 2

Unknown sub-TLV types are to

When the TLV is being processed by a BGP speaker that will be
performing encapsulation, any unknown sub-TLVs MUST be ignored and skipped upon receipt.
skipped. However if the TLV is understood, the entire TLV MUST NOT be
ignored just because it contains an unknown sub-TLV.

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Sub-TLV Length (1 octet): the total number of octets of the sub-TLV
value field.

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Sub-TLV Value (variable): Encodings of the value field depend on the
sub-TLV type as enumerated above. The following sub-sections define
the encoding in detail.

4.1. Encapsulation sub-TLV

The syntax and semantics of the encapsulation sub-TLV is determined
by the tunnel type of the TLV that contains this sub-TLV.

When the tunnel type of the TLV is L2TPv3, the following is the
structure of the value field of the encapsulation sub-TLV:

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Session ID (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Cookie (Variable) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

* Session ID: a 4-octet value locally assigned by the advertising
router that serves as a lookup key in the incoming packet's
context.

* Cookie: an optional, variable length (0 to 64 bits) value used by
L2TPv3 to check the association of a received data message with
the session identified by the Session ID. The Cookie value is
tightly coupled with the Session ID.

The length of the cookie is not encoded explicitly, but can be
calculated as: (sub-TLV length - 4)

When the tunnel type of the TLV is GRE, the following is the
structure of the value field of the encapsulation sub-TLV:

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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| GRE Key (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

* GRE Key: A 4 Octet field that is generated by the advertising
router. The actual method by which the key is obtained is beyond
the scope of the document. The key is inserted into the GRE
encapsulation header of the payload packets sent by ingress
routers to the advertising router. It is intended to be used for
identifying extra context information about the received payload.

Note that the key is optional. Unless a key value is being
advertised, the GRE encapsulation sub-TLV MUST NOT be present.

4.2. Protocol Type sub-TLV

The protocol type sub-TLV encodes MAY be encoded to indicate the type of the
payload packets that will be encapsulated with the tunnel parameters
being signaled in the TLV. The value field of the sub-TLV contains a
2-octet protocol type that is one of the types defined in [IANA-AF]
as ETHER TYPEs.

As an

For example, if we want to use three L2TPv3 sessions, one carrying
IPv4 packets, one carrying IPv6 packets, and one carrying MPLS
packets, the egress router will include three TLVs of L2TPv3
encapsulation type, each specifying a different session id and a
different payload type. The protocol type sub-TLV for these will be
IPv4 (protocol type = 0x0800), IPv6 (protocol type = 0x86dd), and
MPLS (protocol type = 0x8847) respectively. This informs the ingress
routers of the appropriate encapsulation information to use with each
of the given protocol types. Insertion of the specified session id at
the ingress routers allows the egress to process the incoming packets
correctly, according to their protocol type.

Note that the protocol type sub-TLV is optional, e.g. if the
tunneling technology is GRE, this sub-TLV is not required.

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4.3. Tunnel Type Selection

A BGP speaker may include multiple tunnel TLVs in the tunnel
attribute. The receiving speaker MAY have local policies defined to
choose different tunnel types for different sets/types of payload
prefixes received from the same BGP speaker. For instance, if a BGP
speaker includes both L2TPv3 and GRE tunnel types in the tunnel
attribute and it also advertises IPv4 and IPv6 prefixes, the ingress
router may have local policy defined to choose L2TPv3 for IPv4

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prefixes (provided the protocol type received in the tunnel attribute
matches) and GRE for IPv6 prefixes.

Additionally, the Encapsulation SAFI UPDATE message can contain a
community or extended-community as a way to color the corresponding
tunnel TLV(s). The same community or extended community can then be
attached to the UPDATE messages that contain payload prefixes. This
way, the BGP speaker can express the fact that it expects the packets
corresponding to these payload prefixes to be received with a
particular tunnel encapsulation header.

In a multi-vendor deployment that has routers supporting different
tunneling technologies, attaching community and/or extended-community
to the Encapsulation SAFI UPDATE message can serve as a
classification mechanism (for example, set A of routers for GRE and
set B of routers for L2TPv3). The ingress router can then choose the
encapsulation data appropriately while sending packets to an egress
router.

These communities/extended communities, if used, will be user defined
and configured locally on the routers.

4.4. BGP Encapsulation Extended Community

We define a BGP opaque extended community that can be attached to BGP
UPDATE messages to indicate the encapsulation protocol to be used for
sending packets from an ingress router to an egress router.
Considering our example from the "Introduction" section, R2 MAY
include this extended community specifying a particular tunnel type
to be used in the UPDATE message that carries route Q to R1. This is
useful if there are no explicit encapsulation information to be
signaled using the encap SAFI for a tunneling protocol (such as GRE
without key).

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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x03 | TBD | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Tunnel Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The value of the high-order octet of the extended type field is 0x03,
which indicates it's transitive. The value of the low-order octet of
the extended type field is TBD.

The last two octets of the value field encode a tunnel type as
defined in this document.

5. Capability advertisement

A BGP speaker that wishes to exchange tunnel endpoint information
must use the Multiprotocol Extensions Capability Code as defined in
[RFC4760], to advertise the corresponding (AFI, SAFI) pair.

6. Security Considerations

If a third party is able to modify any of the information that is
used to form encapsulation headers, or to choose a tunnel type, or to
choose a particular tunnel for a particular payload type, user data
packets may end up getting misrouted, misdelivered, and/or dropped.

7. IANA Considerations

This document defines a new NLRI format, called Encapsulation NLRI,
to be carried in BGP using multiprotocol extensions. It is to be
assigned its own SAFI.

This document defines a new BGP optional transitive attribute, attribute type,
called Tunnel attribute. attribute and a new opaque extended community sub-type.
These values are to be assigned by IANA.

This document introduces Tunnel TLVs and sub-TLVs. The type space for

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both of these should be set up by IANA as a registry of 2-octet
tunnel types and 1-octet sub-TLV types. These should be assigned on a
first-come- first-serve basis.

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8. Acknowledgements

This specification builds on prior work by Gargi Nalawade, Ruchi
Kapoor, Dan Tappan, David Ward, Scott Wainner, Simon Barber, and
Chris Metz. The current authors wish to thank all these authors for
their contribution.

The authors would like to thank John Scudder, Robert Raszuk, Keyur
Patel, and Chris Metz Metz, and Yakov Rekhter for their valuable comments and
suggestions.

9. Normative References

[RFC4271] Rekhter, Y., Li T., and Hares S.(editors), "A Border
Gateway Protocol 4 (BGP-4)," RFC 4271, January 2006.

[RFC4760] Bates et al, "Multiprotocol Extensions for BGP-4," RFC
4760, January 2007.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels," March 1997.

[IANA-AF] "Address Family Numbers," Reachable from
http://www.iana.org/numbers.html

10. Informative References

[SOFTWIRE] Dawkins S. (editor), "Softwire Problem Statement," draft-
ietf-softwire-problem-statement-02.txt, May 2006.

[Softwires-Mesh-Frame-work] Wu, J. et al, "Softwire Mesh Framework,"
draft-ietf-softwire-mesh-framework-01.txt, June 2007.

11. Authors' Addresses

Pradosh Mohapatra
Cisco Systems, Inc.
170 Tasman Drive
San Jose, CA, 95134
Email: pmohapat@cisco.com

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Eric Rosen
Cisco Systems, Inc.
1414 Massachusetts Avenue
Boxborough, MA, 01719
E-mail: erosen@cisco.com

12. Full Copyright Statement

This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.

This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
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OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
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ipr@ietf.org.

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