WDIFF

draft-ietf-ngtrans-isatap-06.txt --> draft-ietf-ngtrans-isatap-07.txt

NGTRANS Working Group F. Templin
INTERNET-DRAFT
Internet-Draft Nokia
Expires: June 13, 2003 T. Gleeson
Cisco Systems K.K.
M. Talwar
D. Thaler
Microsoft Corporation

Expires 31 April 2003 31 October
December 13, 2002

Intra-Site Automatic Tunnel Addressing Protocol (ISATAP)

draft-ietf-ngtrans-isatap-06.txt
draft-ietf-ngtrans-isatap-07.txt

Status of this Memo

This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.

Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on June 13, 2003.

Abstract

This document specifies the an Intra-Site Automatic Tunnel Addressing
Protocol (ISATAP) that connects IPv6 hosts and routers (nodes) within IPv4
sites. ISATAP is a transition mechanism that enables incremental
deployment of IPv6 by treating treats the site's IPv4
infrastructure as a Non-Broadcast Multiple Access (NBMA) link layer
for IPv6. ISATAP
mechanisms use an IPv6 interface identifier format that embeds an with no requirement for IPv4 address - this multicast. ISATAP enables
intra-site automatic IPv6-in-IPv4 tunneling within a
site, whether the site uses globally assigned
or private IPv4
addresses. The new interface identifier format can be used with both
local and global unicast IPv6 prefixes - this enables IPv6 routing
both locally and globally. ISATAP mechanisms introduce no impact on addresses are used.

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routing table size and require no special IPv4 services (e.g., IPv4
multicast).

1. Introduction

This document presents a simple approach that enables incremental
deployment of IPv6 [1] within IPv4-based [2] sites in a manner that
is com-
patible compatible with inter-domain transition mechanisms, e.g., [6TO4]. RFC 3056
(6to4) [17]. We refer to this approach as the Intra-Site Automatic
Tunnel Addressing Protocol, or ISATAP (pronounced: "ice-a-tap").
ISATAP allows dual-
stack dual-stack nodes that do not share a common link with
an IPv6 router to automatically tunnel packets to the IPv6 next-hop
address through IPv4, i.e., the site's IPv4 infrastructure is treated
as an NBMA link layer.

This document specifies details for the transmission of IPv6 packets
over ISATAP links (i.e., automatic IPv6-in-IPv4 tunneling), including
a new EUI-64 [EUI64] based interface identifier [ADDR][AGGR] format [3][4][5] that embeds
an IPv4 address. This format supports configuration of global,
site-local and link-local addresses as specified in [AUTO] RFC 2462 [6] as
well as simple link-layer address mapping. Simple validity checks
for received packets are given. Also specified in this document is
the operation of IPv6 Neighbor Discovery for ISATAP, as permitted for
NBMA links by [DISC]. RFC 2461 [7]. The document finally presents deployment
and security considerations for ISATAP.

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2. Applicability Statement

ISATAP provides the following features:

o treats site's IPv4 infrastructure as an NBMA link layer using
automatic IPv6-in-IPv4 tunneling (i.e., no configured tunnel
state)

o enables incremental deployment of IPv6 hosts within IPv4 sites
with no aggregation scaling issues at border gateways

o requires no special IPv4 services within the site (e.g.,
multicast)

o supports both stateless address autoconfiguration and manual
configuration

o supports networks that use non-globally unique IPv4 addresses
(e.g., when private address allocations [PRIVATE] [8] are used), but does
not allow the virtual ISATAP link to span a Network Address
Translator [NAT] [9]

o compatible with other NGTRANS mechanisms (e.g., 6to4 [17])

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- compatible with other NGTRANS mechanisms (e.g., [6TO4])

3. Terminology

The terminology of [IPv6] RFC 2460 [1] applies to this document. The
following additional terms are defined:

link:
same definition as [AUTO][DISC]. [6][7].

underlying link:
a link layer that supports IPv4 (for ISATAP), and MAY also support
IPv6 natively.

ISATAP link:
one or more underlying links used for IPv4 tunneling. The IPv4 network
layer addresses of the underlying links are used as link-layer
addresses on the ISATAP link.

ISATAP interface:
a node's attachment to an ISATAP link.

ISATAP prefix:
a prefix used to configure an address on the ISATAP interface.
This prefix is administratively assigned to the ISATAP link and
MUST NOT be duplicated on native IPv6 links.

ISATAP address:
an IPv6 address with an ISATAP prefix and an ISATAP format
interface identifier constructed as specified in section 4.

ISATAP router:
an IPv6 node that has an ISATAP interface over which it forwards
packets not explicitly addressed to itself.

ISATAP host:
any node that has an ISATAP interface and is not an ISATAP router.

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4. Transmission of IPv6 Packets on ISATAP Links

ISATAP links transmit IPv6 packets via automatic tunneling tunnels using the
site's IPv4 infrastructure as an NBMA link layer. Automatic tunneling
for ISATAP uses the same encapsulation, hop limit, IPv4 header con-
struction, and decapsualtion specifications in [MECH, 3], i.e., IPv6
packets are automatically encapsulated in IPv4 using 'ip-protocol-41'
as the payload type number. The specifications in [MECH, 3.2, 3.4] do

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not apply for ISATAP; instead:

- The default link MTU SHOULD be set to the minimum IPv6 MTU of
1280 bytes [IPV6], unless specific configuration information
is available. The Don't Fragment bit SHOULD NOT be set in the
encapsulating IPv4 header.

- IPv4 ICMP errors
and ARP failures may be processed as link error notifications, as
allowed by [DISC]

Specific RFC 2461 [7]. The common tunneling mechanisms specified
in Section 3 of RFC 2893 [10] are used, with the following noted
specific considerations for ISATAP links are given below:

4.1. and automatic tunnels:

4.1 ISATAP Interface Identifier Construction

IPv6 unicast addresses [ADDR][AGGR] [3][4] include a 64-bit interface iden-
tifier identifier
field in "modified EUI-64 format", based on the IEEE EUI-64
[EUI64] [5]
specification. (Modified EUI-64 format inverts the sense of the 'u/l' 'u/
l' bit from its specification in [EUI64], [5], i.e., 'u/l' = 0 indicates
local-use.) ISATAP interface identifiers are constructed by
prepending the 32-bit string '00-00-5E-FE' with an IPv4 address (see
the following section for examples). Appendix B includes text
explaining the rationale for this construction rule.

4.2.

4.2 Stateless Autoconfiguration and Link-Local Addresses

ISATAP addresses are unicast addresses [ADDR,2.5] that use ISATAP format
interface identifiers as follows:

Figure 1

Link-local, site-local, and global ISATAP addresses can be created
exactly as specified in [ADDR], [3], (e.g., by auto-configuration [AUTO] [6] or
manual configuration). For example, the IPv6 address:

3FFE:1A05:510:1111:0:5EFE:8CAD:8108

has a prefix of '3FFE:1A05:510:1111::/64' and an ISATAP format inter-
face
interface identifier with embedded IPv4 address: '140.173.129.8'.
The address is alternately written as:

3FFE:1A05:510:1111:0:5EFE:140.173.129.8

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The link-local and site-local variants (respectively) are:

FE80::0:5EFE:140.173.129.8

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FEC0::1111:0:5EFE:140.173.129.8

4.3.

4.3 ISATAP Link/Interface Configuration

A node configures an

An ISATAP link over consists of one or more underlying links that support
IPv4
links, i.e., the for tunneling within a site.

ISATAP link MAY be interfaces are configured over one or more link-
layer (IPv4) addresses. Each link-layer ISATAP links; each IPv4 address 'V4ADDR_LINK' is used
assigned to configure a link-local address 'FE80::0:5EFE:V4ADDR_LINK' on an
ISATAP interface. ISATAP interfaces MAY be assigned one per link-
layer address, or underlying link is seen as a single interface link-layer address for multiple
ISATAP.

At least one link-layer
addresses.

In the former case, the address of per each ISATAP router interface
SHOULD be added to the Potential Routers List (see section Section 5.2.1). In the lat-
ter case, the interface will accept ISATAP packets addressed to any
of the IPv4 link-layer addresses, but will choose one as its primary
address, used for sourcing packets. Only this address need be repre-
sented in the Potential Routers List.

4.4.

4.4 Sending Rules and Address Mapping

The IPv6 next-hop address for packets sent on an ISATAP link MUST be
an ISATAP address. Packets that do not satisfy this constraint MUST
be discarded and an ICMP ICMPv6 destination unreachable indication with
code 3 (Address Unreachable) [ICMPv6] [11] MUST be returned. No other sending
rules are necessary.

The procedure for mapping unicast addresses into link-layer addresses
is to simply treat the last four octets of the ISATAP address as an
IPv4 address (in network byte order). No multicast address mappings
are specified.

4.5.

4.5 Validity Checks for Received Packets

Packets received on ISATAP interfaces MUST satisfy at least one
(i.e., one or both) of the following validity checks:

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o the network-layer (IPv6) source address has a prefix configured on
the ISATAP interface and an ISATAP-format interface identifier
that embeds the link-layer (IPv4) source address, i.e., source is
on-link

o the link-layer (IPv4) source address is an "active" member of in the Potential Routers
List (see section 5.2), Section 5.2.1), i.e., previous hop is an on-link ISATAP
router actively being used by the node

Packets that do not satisfy at least one of the above checks are
silently discarded.

5. Neighbor Discovery for ISATAP Links

Section 3.2 of [DISC] ("Supported Link Types") provides the following
guidelines for non-broadcast multiple access (NBMA) link support:

"Redirect, Neighbor Unreachability Detection

4.6 Tunnel MTU and next-hop determi-
nation should Fragmentation

ISATAP interfaces implement automatic tunnels that may be implemented as described in this document. Address
resolution and the mechanism for delivering Router Solicitations
and Advertisements on NBMA links is not specified in this docu-
ment." configured

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over multiple underlying links with diverse MTUs. The ISATAP
interface MTU (ISATAP_MTU) SHOULD implement Redirect, Neighbor Unreachability
Detection, and next-hop determination exactly as specified in [DISC].
Address resolution and be no larger than the mechanisms for delivering Router Solicita-
tions and Advertisements for ISATAP links are not specified by
[DISC]; instead, they are specified in this document. (Note that
these mechanisms MAY potentially apply to other types largest MTU
of NBMA all underlying links
in the future.)

5.1. Address (LINK_MTU), minus 20 bytes for IPv4
encapsulation.

The minimum value (ISATAP_MINMTU) MUST be at least 1280 bytes [1],
but SHOULD be set to 1380 bytes (see note 1). The maximum value used
for ISATAP_MTU SHOULD be 4140 bytes (see note 2). The maximum
receive unit (ISATAP_MRU) MUST be at least 4400 bytes.

IPv6 path MTU discovery [12] is required for IPv6 interfaces that
send packets larger than 1280 bytes. The following considerations
for ISATAP interfaces are noted:

o ISATAP encapsulators and decapsulators are IPv6 neighbors since
they share a common link layer, i.e., the ISATAP link

o ISATAP neighbors may be separated by multiple IPv4 hops requiring
IPv4 path MTU discovery [13] to establish per-neighbor MTUs
(NBR_MTU)

o NBR_MTU information is stored as link-layer (IPv4) information
(e.g., in the IPv4 path MTU discovery cache), thus it may not be
visible to upper layers in all implementations

o NBR_MTU information may not always be available for each neighbor
due to finite storage limitations

o IPv4 path MTU discovery delivers ICMPv4 "fragmentation needed"
messages, but these cannot be translated into ICMPv6 "packet too
big" messages. Thus, encapsulated packets MUST be sent with the
DF flag in the IPv4 header NOT set unless additional state is
maintained in the encapsulator (see note 3)

Traditional packetization and network (IPv6) layer implementations
view ISATAP interfaces as ordinary IPv6 interfaces with a single MTU
(ISATAP_MTU). Such implementations forward only those IPv6 packets
of size ISATAP_MTU or smaller to the ISATAP interface. All other
packets are dropped, and an IPv6 ICMP "packet too big" message with
MTU = ISATAP_MTU is returned.

Modified packetization and network (IPv6) layer implementations MAY
look into the ISATAP link layer for per-neighbor MTU information.
When available, this information supersedes ISATAP_MTU in determining
whether to forward the packet or return an ICMPv6 "packet too big"
(see above).

For IPv6 packets forwarded to the ISATAP interface, all

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implementations employ the following algorithm at the link layer to
determine when to perform IPv6-in-IPv4 encapsulation and when to
return an IPv6 ICMP "packet too big" message:

Determine per-neighbor LINK_MTU; NBR_MTU, e.g., by consulting IPv4
forwarding table and/or IPv4 path MTU discovery cache, then:

if NBR_MTU information exists
if packet is larger than NBR_MTU - 20 and packet
is larger than ISATAP_MINMTU
Send IPv6 ICMP "packet too big" with
MTU = MAX(NBR_MTU - 20, ISATAP_MINMTU)
Drop packet
else
Encapsulate but do not set the Don't Fragment
flag in the IPv4 header
endif
else
if packet is larger than LINK_MTU - 20 and packet is
larger than ISATAP_MINMTU
Send IPv6 ICMP "packet too big" with
MTU = ISATAP_MINMTU
Drop packet
else
if IPv6 neighbor is an IPv4 neighbor on the
underlying link, or packet is less than
or == ISATAP_MINMTU</t>
Encapsulate but do not set the Don't
Fragment flag in the IPv4 hdr
else
send ICMPv6 "packet too big" with
MTU = ISATAP_MINMTU
Drop packet
endif
endif
endif

Figure 2

NOTES:

1. Nearly all IPv4 routers can forward 1500 byte packets without
fragmentation. However, sub-IPv4 layer encapsulation (e.g., for
VPNs) may occur on some paths. Commonly-deployed VPNs use an MTU
of 1400 bytes, thus 1380 bytes SHOULD be used as ISATAP_MINMTU.

2. TCP adapts to an overestimated MSS by reducing the segment size
based on IPv6 "packet too big" messages ([12], section 5.4), thus

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setting ISATAP_MTU to the largest MTU of all underlying links
would optimize performance for asymmetric paths.

SCTP ([14], section 7.3) and other packetization layers ([12],
section 5.5), perform upper-layer fragmentation based on IPv6
"packet too big" messages, which may result in unacceptable loss
when the initial MTU estimate is too large.

4140 is the RECOMMENDED maximum value for ISATAP_MTU, since:

* 4140 bytes makes efficient use of common larger-than- ethernet
MTUs in the internet (e.g., FDDI)

* Locally-generated ICMPv6 "packet too big" messages are likely
to advertise an MTU of 1380, resulting in at most three
fragments and limiting loss probability

3. Implementations MAY cache recently-sent IPv6 packets to provide
state for translating ICMPv4 "fragmentation needed" messages into
ICMPv6 "packet too big" messages. Such implementations MAY set
the DF flag in the IPv4 header in the above algorithm for packets
that will be retained in the cache at least as long as the
round-trip time (RTT) between the encapsulator and decapsulator.

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5. Neighbor Discovery for ISATAP Links

Section 3.2 of RFC 2461 [7] provides the following guidelines for
non-broadcast multiple access (NBMA) link support:

"Redirect, Neighbor Unreachability Detection and next-hop
determination should be implemented as described in this document.
Address resolution and the mechanism for delivering Router
Solicitations and Advertisements on NBMA links is not specified in
this document."

ISATAP links SHOULD implement Redirect, Neighbor Unreachability
Detection, and next-hop determination exactly as specified in [7].
Address resolution and the mechanisms for delivering Router
Solicitations and Advertisements for ISATAP links are not specified
by [7]; instead, they are specified in this document. (Note that
these mechanisms MAY potentially apply to other types of NBMA links
in the future.)

5.1 Address Resolution

Protocol addresses (IPv6) in ISATAP are resolved to link-layer
addresses (IPv4) by a static computation, i.e., the last four octets
are treated as an IPv4 address.

ISATAP nodes hosts SHOULD enhance the static address resolution computation
with a unicast Neighbor Solicitation(NS)/Neighbor Advertisement(NA)
exchange to ensure IPv6 level reachability of the neighbor and also
SHOULD perform Neighbor Unreachability Detection (NUD) as specified
in [DISC, 7.3], (RFC 2461 [7], section 7.3). ISATAP routers MAY implement the
enhanced address resolution and NUD, but this might not scale in all
environments. All ISATAP nodes MUST send solicited neighbor adver-
tisements as specified in [DISC, 7.2.4].

The link-layer address option used in [DISC] is not needed. Link-
layer
advertisements ([7], section 7.2.4).

Link-layer address options ([7], section 4.6.1) for this
specification MUST have Length = 1 and a six-octet interface
identifier consisting of two zero octets followed by a four-octet
IPv4 address. Options of this form SHOULD NOT be sent in any Neighbor Discovery
packets, NS/NA
messages and MUST be silently ignored in any received Neighbor Dis-
covery packets.

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5.2. NS/NA messages.

5.2 Router and Prefix Discovery

Since the site's IPv4 infrastructure is treated as an NBMA link
layer, unsolicited Router Advertisements do not provide sufficient
means for router discovery on ISATAP links. Thus, alternate mecha-
nisms
mechanisms are required and specified below:

5.2.1.

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5.2.1 Conceptual Data Structures

ISATAP nodes use the conceptual data structures Prefix List and
Default Router List exactly as specified in [DISC,5.1]. ([7], section 5.1). ISATAP links
add a new conceptual data structure "Potential Router List" and the
following new configuration variable:

ResolveInterval
Time between name service resolutions. Default and suggested
minimum: 1hr

A Potential Router List (PRL) is associated with every ISATAP link.
The PRL provides context for router discovery and a trust basis for router validation (see security
considerations). Each entry in the PRL has an IPv4 address and an
associated timer used for polling. timer. The IPv4 address represents a router's ISATAP
interface (likely to be an "advertising interface"), and is used to
construct the ISATAP link-
local link-local address for that interface. The
following sections specify the process for initializing the PRL:

When a node enables an ISATAP link, it initializes first discovers a DNS (RFC
1035 [20]) fully-qualified domain name for the Potential
Router List (PRL) site's ISATAP service.
The domain name MAY be established by a DHCPv4 [15] option for that link. Unless other information is avail-
able (e.g., ISATAP
(option code TBD, see IANA Considerations), by manual address configuration, a vendor-specific DHCP
option, etc.) the following method (similar to the [SIP, 1.4.2] pro-
cedure) SHOULD be used:

1.
or by an unspecified alternative method. The site administrator maintains address records DHCPv4 option for
ISATAP
router interfaces, and makes these available is implemented exactly as in RFC 3361 [16] with the site's
name service. Nodes attempt to find one or more addresses
for following
noted exceptions:

o the PRL by querying DHCP option code for ISATAP (TBD) is used

o the name service.

2. There encoding byte MUST be 0, i.e.; only FQDNs are no mandatory rules on the selection of accepted

o if multiple domain name
to be names occur, only the first is used within a site for this purpose, but administrators
are encouraged to use

Next, the node initializes the link's PRL with IPv4 addresses
associated with the "isatap.domainname" convention
(e.g., isatap.example.com), as specified in [RFC2219]. Nodes
can construct this domain name discovered above. IPv4 addresses are
discovered through manual config or by prepending querying the label "isatap" name service to their parent domain name, which is established by other
means. Nodes then query this
resolving the domain name for into address records (e.g., DNS 'A'
resource records), and initialize the PRL with records) containing IPv4 addresses. Unspecified alternative
methods may also be used.

Notes:

1. Site administrators maintain a domain name for the ISATAP service
and a list of IPv4 addresses representing ISATAP router
interfaces (normally as address records in the replies.

3. After initialization, nodes periodically repeat site's name
service). Administrators may also advertise the above domain name in a
DHCPv4 option for ISATAP.

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procedure ResolveInterval

2. There are no mandatory rules for the selection of a domain name,
but administrators are encouraged to update use the PRL with any IPv4
addresses added/deleted since convention
"isatap.domainname" (e.g., isatap.example.com).

3. After initialization, nodes periodically re-initialize the previous iteration. PRL
(after ResolveInterval). When DNS is used, nodes MUST follow the procedures in [RFC1035]
regarding
cache invalidation procedures in [20] when the DNS time-to-live
expires.

5.2.2. Validation of

5.2.2 Validity Checks for Router Advertisement Messages Advertisements

A node MUST silently discard any received Router Advertisement mes-
sages messages it
receives that do not satisfy both the validity checks in [DISC,6.1.2] as well
as ([7],
section 6.1.2) and the following additional validity check for
ISATAP:

o the network-layer (IPv6) source address is derived from an ISATAP address and
embeds an IPv4 address in from the PRL

5.2.3.

5.2.3 Router Specification

Advertising ISATAP interfaces of routers behave the same as advertis-
ing
advertising interfaces described in [DISC,6.2]. ([7], section 6.2). However,
periodic unsolicited multicast Router Advertisements are not
required, thus the "interval timer" associated with advertising
interfaces is not used for that purpose.

When an ISATAP router receives a valid Router Solicitation on an
advertising ISATAP interface, it replies with a unicast Router Adver-
tisement
Advertisement to the address of the node which sent the Router Solicita-
tion.
Solicitation. The source address of the Router Advertisement is a
link-local unicast address associated with the interface. This MAY
be the same as the destination address of the Router Solicitation.
ISATAP routers MAY engage in the polling solicitation process described under
Host Specification
below (e.g. below, e.g., if Router Advertisement consistency
verification
[DISC,6.2.7] is desired), but this ([7], section 6.2.7) is not required.

5.2.4. desired.

5.2.4 Host Specification

All entries in the PRL are assumed to represent active ISATAP routers
within the site, i.e., the PRL provides trust basis only; not
reachability detection. Hosts periodically poll solicit information from
one or more entries in the PRL ("PRL(i)") by sending unicast Router
Solicitation messages using the IPv4 address ("V4ADDR_PRL(i)") and
associated timer in the entry. Hosts add the following variable to
support the polling solicitation process:

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MinRouterSolicitInterval
Minimum time between sending Router Solicitations to any router.
Default and suggested minimum: 15min

When a PRL(i) is selected for polling, selected, the host sets its associated timer to
MinRouterSolicitInterval and initiates polling solicitation following a short
delay as for initial solicitations [ND,6.3.7]), and in ([7], section 6.3.7). The solicitation process repeats
when the

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Polling

Solicitation consists of sending Router Solicitations to the ISATAP link-
local
link-local address constructed from the entry's IPv4 address, i.e.,
they are sent to 'FE80::0:5EFE:V4ADDR_PRL(i)' instead of 'All-Routers mul-
ticast'.
multicast'. They are otherwise sent exactly as in the same manner described in
[DISC,6.3.7].

When the host receives a valid ([7], section
6.3.7).

Hosts process received Router Advertisement (i.e., one that
satisfies the validity checks in sections 4.5 and 5.2.2) it is pro-
cesses in the same manner described Advertisements exactly as in [DISC,6.3.4]. The host addi-
tionally resets ([7],
section 6.3.4). Hosts additionally reset the timer associated with
the V4ADDR_PRL(i) embedded in the network-layer source address in the
each received Router Advertisement. The timer is reset to either 0.5
* (the minimum value in the router life-
time lifetime or valid lifetime of any
on-link prefixes advertised) or Min-
RouterSolicitInterval; MinRouterSolicitInterval; whichever
is longer. longer.

([7], section 6.3.4) includes the following specification:

"To limit the storage needed for the Default Router List, a host
MAY choose not to store all of the router addresses discovered via
advertisements. However, a host MUST retain at least two
addresses and SHOULD retain more."

The router solicitation process for ISATAP nodes is analogous to
choosing which router addresses to store as in the above text.
ISATAP nodes may wish to consider the control traffic overhead of
this process when choosing how many routers to solict. The manner of
choosing particular routers in the PRL for solicitation is outside
the scope of this specification.

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6. ISATAP Deployment Considerations

6.1.

6.1 Host And Router Deployment Considerations

For hosts, if an underlying link supports both IPv4 (over which ISA-
TAP
ISATAP is implemented) and also supports IPv6 natively, then ISATAP
MAY be enabled if the native IPv6 layer does not receive Router Adver-
tisements
Advertisements (i.e., does not have connection with an IPv6 router).
After a non-link-local address has been configured and a default
router acquired on the native link, the host SHOULD discontinue the 'Router
Polling Process'
router solicitation process specified described in section 5.2.4 the host specification and
allow exist-
ing existing ISATAP address configurations to expire as specified
in
[DISC,5.3][AUTO,5.5.4]. ([7], section 5.3) and ([6], section 5.5.4). Any ISATAP addresses
added to the DNS for this host should also be removed. In this way,
ISATAP use will gradu-
ally gradually diminish as IPv6 routers are widely
deployed throughout the site.

Routers MAY configure an interface to simultaneously support both
native IPv6, and also ISATAP (over IPv4). Routing will operate as
usual between these two domains. Note that the prefixes used on the
ISATAP and native IPv6 interfaces will be distinct. The IPv4
address(es) configured on a router's ISATAP interface(s) SHOULD be
added (either automatically or manually) to the site's address
records for ISATAP router interfaces (see section 5.2.1).

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6.2. interfaces.

6.2 Site Administration Considerations

The following considerations are noted for sites that deploy ISATAP:

o ISATAP links are administratively defined by a set of router
interfaces, and set of nodes which have those interface addresses
in their potential router lists. Thus, ISATAP links are defined
by administrative (not physical) boundaries.

o ISATAP hosts and routers can be deployed in an ad-hoc and
independent fashion. In particular, ISATAP hosts can be deployed
with little/no advanced knowledge of existing ISATAP routers, and
ISATAP routers can deployed with no reconfiguration requirements
for hosts.

o ISATAP nodes periodically send Router Solicitations (RS) to all entries
in the Potential Router List. Worst-case control traffic is on the
order of (M x N), where 'M' is the number one or
more members of routers in the Potential potential router list. When Router List and 'N' is
Advertisements (RAs) are received, the total number of nodes on Router Lifetime value
provides a timer for the ISATAP link.
The MinRouterSolicitInterval ([5.2.4]) bounds control traffic next RS to be sent. Worst-case is for
large numbers
small values of nodes even in worst-case scenarios.

- Router Lifetime which is bounded by
MinRouterSolicitInterval.

o ISATAP nodes periodically refresh the entries on the PRL,

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typically by polling querying the DNS. Responsible site administration
can reduce the control traffic. At a minimum, administrators
SHOULD ensure that the site's address records for ISATAP router
interfaces (see
section 5.2.1) are well maintained.

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7. IANA considerations Considerations

A DHCPv4 option assignment for ISATAP is requested, as outlined in
the procedures found in RFC 2939 [21], section 3.

Appendix B offers one possible proposes a specification for managing the IEEE OUI
assigned to IANA for EUI-64 interface identifier construction. This
specification is made freely available to IANA for any purpose they
may find useful.

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8. Security considerations

Site administrators are advised that, in addition to possible attacks
against IPv6, security attacks against IPv4 MUST also be considered.
Many security considerations in [6OVER4,9] RFC 2529 [18], section 9 apply also
to ISATAP.

Responsible IPv4 site security management is strongly encouraged. In
particular, border gateways SHOULD implement filtering to detect
spoofed IPv4 source addresses at a minimum; ip-protocol-41 filtering
SHOULD also be implemented.

If IPv4 source address filtering is not correctly implemented, the

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ISATAP 31 October 2002 validity checks in section 4.7 will not be effective in preventing IPv6
source address spoofing.

If filtering for ip-protocol-41 is not correctly implemented, IPv6
source address spoofing is clearly possible, but this can be elimi-
nated
eliminated if both IPv4 source address filtering, and the ISATAP
validity checks
in section 4.7 are implemented.

[DISC,6.1.2]

(RFC 2461 [7]), section 6.1.2 implies that nodes trust Router
Advertisements they receive from on-link routers, as indicated by a
value of 255 in the IPv6 'hop-limit' field. Since this field is not
decremented when ip-
protocol-41 ip-protocol-41 packets traverse multiple IPv4 hops [MECH,3.3],
([10], section 3), ISATAP links require a different trust model. In
particular, ONLY those Router Advertisements received from a member
of the Potential Routers List are trusted; all others are silently discarded (see section
5.2.2).
discarded. This trust model is predicated on IPv4 source address filter-
ing,
filtering, as described above.

The ISATAP address format does not support privacy extensions for
stateless address autoconfiguration [PRIVACY]. [19]. However, since the ISATAP
interface identifier is derived from the node's IPv4 address, ISATAP
addresses do not have the same level of privacy concerns as IPv6
addresses that use an interface identifier derived from the MAC
address. (This issue is the same for NAT'd addresses.)

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9. Acknowledgements

Some of the ideas presented in this draft were derived from work at
SRI with internal funds and contractual support. Government sponsors
who supported the work include Monica Farah-Stapleton and Russell
Langan from U.S. Army CECOM ASEO, and Dr. Allen Moshfegh from U.S.
Office of Naval Research. Within SRI, Dr. Mike Frankel, J. Peter Mar-
cotullio,
Marcotullio, Lou Rodriguez, and Dr. Ambatipudi Sastry supported the
work and helped foster early interest.

The following peer reviewers are acknowledged for taking the time to
review a pre-release of this document and provide input: Jim Bound,
Rich Draves, Cyndi Jung, Ambatipudi Sastry, Aaron Schrader, Ole
Troan, Vlad Yasevich.

The authors acknowledge members of the NGTRANS community who have
made significant contributions to this effort, including Rich Draves,
Alain Durand, Nathan Lutchansky, Karen Nielsen, Art Shelest, Margaret
Wasserman, and Brian Zill.

The authors also wish to acknowledge the work of Quang Nguyen [VET] [22]
under the guidance of Dr. Lixia Zhang that proposed very similar
ideas to those that appear in this document. This work was first
brought to

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INTERNET-DRAFT ISATAP 31 October 2002 the authors' attention on September 20, 2002.

Finally, the authors recognize that ideas similar to those in this
document may have already been presented by others and wish to
acknowledge any other such contributions.

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Normative References

[ADDR]

[1] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6)
Specification", RFC 2460, December 1998.

[2] Postel, J., "Internet Protocol", STD 5, RFC 791, September
1981.

[3] Hinden, R., R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 2373, July 1998. (Pending approval
of "addr-arch-v3").

[AGGR] Hinden., R, O'Dell, M.,

[4] Hinden, R. and S. Deering, S., "An IPv6 Aggregatable Global Unicast
Address Format", RFC 2374, July 1998.

[AUTO]

[5] IEEE, "http://standards.ieee.org/regauth/oui/tutorials/
EUI64.html", March 1997.

[6] Thomson, S., S. and T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC 2462, December 1998.

[DISC]

[7] Narten, T., Nordmark, E., E. and W. Simpson, "Neighbor Discovery
for IP Version 6 (IPv6)", RFC 2461, December 1998.

[EUI64] IEEE, "Guidelines

[8] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G. and E.
Lear, "Address Allocation for 64-bit Global Identifier (EUI-64)
Registration Authority",
http://standards.ieee.org/regauth/oui/tutori-
als/EUI64.html,
March 1997.

[ICMPv6] Private Internets", BCP 5, RFC
1918, February 1996.

[9] Egevang, K. and P. Francis, "The IP Network Address Translator
(NAT)", RFC 1631, May 1994.

[10] Gilligan, R. and E. Nordmark, "Transition Mechanisms for IPv6
Hosts and Routers", RFC 2893, August 2000.

[11] Conta, A. and S. Deering, "Internet Control Message Protocol
(ICMPv6) for the Internet Protocol Version 6 (IPv6)
Specification", RFC 2463, December 1998.

[IPV4] Postel,

[12] McCann, J., "Internet Protocol", RFC 791.

[IPV6] Deering, S., and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460.

[MECH] Gilligan, R., S. and E. Nordmark, "Transition Mechanisms J. Mogul, "Path MTU Discovery for
IPv6 Hosts and Routers",
IP version 6", RFC 2893, 1981, August 2000.

[NAT] Egevang, K., 1996.

[13] Mogul, J. and P. Francis, "The IP Network Address
Translator (NAT)", S. Deering, "Path MTU discovery", RFC 1631, May 1994.

[PRIVATE] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G., 1191,
November 1990.

[14] Stewart, R., Xie, Q., Morneault, K., Sharp, C., Schwarzbauer,
H., Taylor, T., Rytina, I., Kalla, M., Zhang, L. and E. Lear, "Address Allocation for Private Internets", V. Paxson,
"Stream Control Transmission Protocol", RFC 1918, February 1996. 2960, October 2000.

[15] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131,

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Internet-Draft ISATAP 31 October December 2002

[SIP] Handley, M.,

March 1997.

[16] Schulzrinne, H., Schooler, E., and
J. Rosenberg, "SIP: "Dynamic Host Configuration Protocol
(DHCP-for-IPv4) Option for Session Initiation Protocol", Protocol (SIP)
Servers", RFC 2543, March 1999. 3361, August 2002.

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Internet-Draft ISATAP December 2002

Informative References

[6OVER4]

[17] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4
Domains without Explicit Tunnels", RFC 2529.

[6TO4] Carpenter, B., and K. Moore, "Connection of IPv6 Domains via
IPv4 Clouds", RFC 3056, February 2001.

[IANA] Reynolds, J.,

[18] Carpenter, B. and J. Postel, "Assigned Numbers", STD 2,
USC/Information Sciences Institute, October 1994.

[PRIVACY] C. Jung, "Transmission of IPv6 over IPv4
Domains without Explicit Tunnels", RFC 2529, March 1999.

[19] Narten, T., T. and R. Draves, "Privacy Extensions for Stateless
Address Autoconfiguration in IPv6", RFC 3041, January 2001.

[RFC1035]

[20] Mockapetris, P., "Domain Names names - Implementation implementation and
Specification",
specification", STD 13, RFC 1035, November 1987.

[RFC2219] Hamilton, M.,

[21] Droms, R., "Procedures and R. Wright, "Use of DNS Aliases IANA Guidelines for
Network Services", Definition of
New DHCP Options and Message Types", BCP 43, RFC 2219 (BCP), October 1997.

[VET] 2939,
September 2000.

[22] Nguyen, Quang, "Virtual Ethernet: A New Approach to
IPv6 Transition", http://irl.cs.ucla.edu/vet/report.ps,
MS Project Report, Spring Q., "http://irl.cs.ucla.edu/vet/report.ps", spring
1998.

Authors

Authors' Addresses

Fred L. Templin
Nokia
313 Fairchild Drive
Mountain View, CA, USA CA 94110
US

Phone: (650)-625-2331
Email: +1 650 625 2331
EMail: ftemplin@iprg.nokia.com

Tim Gleeson
Cisco Systems K.K.
Shinjuku Mitsu Building
2-1-1 Nishishinjuku, Shinjuku-ku
Tokyo 163-0409, JAPAN
email: 163-0409
Japan

EMail: tgleeson@cisco.com

Mohit Talwar
Microsoft Corporation

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Internet-Draft ISATAP 31 October December 2002

Mohit Talwar
Microsoft Corporation
One Microsoft Way
Redmond, WA WA> 98052-6399
US

Phone: +1 425 705 3131
EMail: mohitt@microsoft.com

Dave Thaler
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052-6399
US

Phone: +1 425 703 8835
EMail: dthaler@microsoft.com

APPENDIX A:

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Appendix A. Major Changes

changes from version 06 to version 07:

o clarified address resolution, Neighbor Unreachability Detection

o specified MTU/MRU requirements

changes from version 05 to version 06:

o Addressed operational issues identified in 05 based on discussion
between co-authors

o Clarified ambiguous text per comments from Hannu Flinck; Jason
Goldschmidt

changes from version 04 to version 05:

o Moved historical text in section 4.1 to Appendix B in response to
comments from Pekka Savola

o Identified operational issues for anticipated deployment scenarios

o Included SRI IPR statement and contact information

o Included reference to Quang Nguyen work

changes from version 03 to version 04:

o Re-wrote section on Potential Router List initialization to
reference existing precedence in other documents

o several minor wording changes based on feedback from the community

changes from version 02 to version 03:

o Added contributing co-authors

o RSs are now sent to unicast addresses rather than
all-routers-multicast

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o Brought draft into better alignment with other IPv6
standards-track documents

o Added applicability statement

changes from version 01 to version 02:

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Internet-Draft ISATAP December 2002

o Cleaned up text and tightened up terminology. terminology

o Changed "IPv6 destination address" to "IPv6 next-hop address"
under "sending rules". rules"

o Changed definition of ISATAP prefix to include link and site-local. site-local

o Changed language in sections 4 and 5

changes from version 00 to version 01:

o Revised draft to require different /64 prefixes for ISATAP
addresses and native IPv6 addresses. Thus, a node's ISATAP
interface is assigned a /64 prefix that is distinct from the
prefixes assigned to any other interfaces attached to the node -
be they physical or logical interfaces. This approach eliminates
ISATAP-specific sending rules presented in earlier draft versions.

o Changed sense of 'u/l' bit in the ISATAP address interface
identifier to indicate "local scope", since ISATAP interface
identifiers are unique only within the scope of the ISATAP prefix.
(See section 4.)

changes from personal draft to version 00:

o Title change to provide higher-level description of field of use
addressed by this draft. Removed other extraneous text.

o Major new section on automatic discovery of off-link IPv6 routers
when IPv6-IPv4 compatibility addresses are used.

APPENDIX B:

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Appendix B. Rationale for Interface Identifier Construction Rules

ISATAP specifies an [EUI64]-format EUI64-format address construction for the Orga-
nizationally-Unique
Organizationally-Unique Identifier (OUI) owned by the Internet
Assigned Numbers Authority [IANA]. (IANA). This format (given below) is used
to con-
struct construct both native [EUI64] EUI64 addresses for general use and modified
EUI-64 format interface identifiers for use in IPv6 unicast
addresses:

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|0 2|2 3|3 3|4 6|
|0 3|4 1|2 9|0 3|
+------------------------+--------+--------+------------------------+
| OUI ("00-00-5E"+u+g) | TYPE | TSE | TSD |
+------------------------+--------+--------+------------------------+

Where the fields are:

OUI IANA's OUI: 00-00-5E with 'u' and 'g' bits (3 octets)

TYPE Type field; specifies interpretation of (TSE, TSD) (1 octet)

TSE Type-Specific Extension (1 octet)

TSD Type-Specific Data (3 octets)

And the following interpretations are specified based on TYPE:

TYPE (TSE, TSD) Interpretation
---- -------------------------
0x00-0xFD RESERVED for future IANA use
0xFE (TSE, TSD) together contain an embedded IPv4 address
0xFF TSD is interpreted based on TSE as follows:

TSE TSD Interpretation
--- ------------------
0x00-0xFD RESERVED for future IANA use
0xFE TSD contains 24-bit EUI-48 intf id
0xFF RESERVED by IEEE/RAC

Figure 3

Thus, if TYPE=0xFE, TSE is an extension of TSD. If TYPE=0xFF, TSE is
an extension of TYPE. Other values for TYPE (hence, (thus, other interpreta-
tions
interpretations of TSE, TSD) are reserved for future IANA use.

The above specification is compatible with all aspects of [EUI64], EUI64,
including support for encapsulating legacy EUI-48 interface identi-
fiers
identifiers (e.g., an IANA EUI-48 format multicast address such as:
'01-00-5E-01-02-03' is encapsulated as: '01-00-5E-FF-FE-01-02-03').
But, as:

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'01-00-5E-01-02-03' is encapsulated as: '01-00-5E-FF-FE-01-02-03').
But, the specification also provides a special TYPE (0xFE) to
indicate an IPv4 address is embedded. Thus, when the first four
octets of an IPv6 interface identifier are: '00-00-5E-FE' (note: the
'u/l' bit MUST be 0) the interface identifier is said to be in
"ISATAP format" and the next four octets embed an IPv4 address
encoded in network byte order.

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Appendix C. INTELLECTUAL PROPERTY

SRI International has notified the IETF of IPR considerations for
some aspects of this specification. For more information consult the
online list of claimed rights.

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Intellectual Property Statement

The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; neither does it represent that it
has made any effort to identify any such rights. Information on the specification also provides a special TYPE (0xFE)
IETF's procedures with respect to indi-
cate an IPv4 address is embedded. Thus, when rights in standards-track and
standards-related documentation can be found in BCP-11. Copies of
claims of rights made available for publication and any assurances of
licenses to be made available, or the first four octets result of an attempt made to
obtain a [ADDR]-compatible IPv6 interface identifier are: '00-00-5E-FE'
(note: general license or permission for the 'u/l' bit MUST use of such
proprietary rights by implementors or users of this specification can
be 0) obtained from the interface identifier is said IETF Secretariat.

The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice
this standard. Please address the information to the IETF Executive
Director.

Full Copyright Statement

This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in "ISATAP format" its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the next four octets embed an IPv4 address
encoded above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in network byte order.

INTELLECTUAL PROPERTY

SRI International has notified any way, such as by removing
the IETF copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of IPR considerations
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.

The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assignees.

This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION

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some aspects of this specification. For more information consult

HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

Funding for the
online list of claimed rights. RFC Editor function is currently provided by the
Internet Society.

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----