WDIFF

draft-ietf-ngtrans-isatap-00.txt --> draft-ietf-ngtrans-isatap-01.txt

SRI International
12 March
17 May 2001

Intra-Site Automatic Tunnel Addressing Protocol (ISATAP)
(Formerly: Connecting IPv6 Nodes within IPv4 Sites)

Placeholder for ISOC copyright.

draft-ietf-ngtrans-isatap-00.txt

draft-ietf-ngtrans-isatap-01.txt

Abstract

This document specifies a method an intra-site automatic tunneling protocol
(ISATAP) for connecting IPv6 hosts and routers (nodes) within
predominantly IPv4-based sites. networks. This method is based on an IPv6-IPv4 compatibility IPv6
aggregatable global unicast address format (described herein) that
embeds the IPv4 address of a node within the EUI-64 format interface identifier of an IPv6
address.
identifier. This document assumes that, during the IPv4 to IPv6 co-
existence and transition phase, many sites will deploy IPv6
incrementally within their IPv4 interior routing domains; especially
those sites which have large and complex pre-existing IPv4
infrastructures. Within such sites, the address format and methods
described in this document will enable IPv6 deployment for nodes that
do not share a common multiple access datalink data link with an IPv6 gateway
within for their site.

While other works in progress in the NGTRANS working group propose
mechanisms for assigning globally-unique IPv6 address prefixes to
sites and methods for inter-domain routing between such sites, the
approach outlined in this memo enables large-scale incremental
deployment of IPv6 for nodes within a site's pre-existing IPv4
infrastructure without incurring aggregation scaling issues at the
border gateways nor requiring site-wide deployment of special IPv4
services such as multicast. The approach proposed by this document
supports IPv6 routing within both the site-local and global IPv6
routing domains as well as automatic IPv6 in IPv4 tunneling across
portions of a site's IPv4 infrastructure which have no native IPv6
support. Moreover, Additionally, this approach supports automatic tunneling
within sites which use non globally-unique IPv4 address assignments,
such as when Network Address Translation [NAT] is used.

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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Internet-Drafts are working documents of the Internet Engineering

Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.

Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet- Drafts as reference
material or to cite them other than as "work in progress."

The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt

The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.

1. Introduction

The IETF NGTRANS working group anticipates an heterogeneous IPv4/IPv6
infrastructure in the near future and thus is chartered to develop
mechanisms to support IPv4/IPv6 coexistence and transition toward
global IPv6 deployment. For the most part, existing NGTRANS
approaches focus on inter-domain routing between IPv6 "islands" islands using
the existing global IPv4 backbone as transit. But, these islands may
themselves consist of comprise complex heterogeneous IPv4/IPv6 networks (e.g.
large academic or commercial campus "intranets") intranets) that require intra-
domain IPv4 to IPv6 transition mechanisms and strategies as well. In
order to address this requirement, this document presents a simple
and scalable approach that enables incremental intra-site deployment of IPv6
nodes within predominantly IPv4-based intranets. We refer to this
approach as the Intra-Site Automatic Tunnel Addressing Protocol, or
ISATAP (pronounced: "ice-a-tap").

The ISATAP approach outlined in this document is based on a new an aggregatable global unicast
address format that carries a standard 64-bit IPv6 address prefix
[ADDR][AGGR] with a specially-constructed 64-bit EUI-
64 EUI-64 Interface
Identifier [EUI64]. The 64-bit This address prefix used by
this format is fully compatible with all existing and emerging prefix
assignment
both native IPv6 and inter-domain NGTRANS routing practices (e.g. [6to4],[6BONE]).
But, the interface identifier in an ISATAP address employs a special
construction using (using the IEEE Organizationally Unique Identifier (OUI)
reserved by the Internet Assigned Numbers Authority [IANA] along with a "type" field
to indicate [IANA]) that the identifier
encapsulates an IPv4 address suitable for automatic intra-domain IPv6-in-IPv4 tunneling. As such, tun-
neling. Since tunneling occurs only within the site-level prefix of
the ISATAP address, the embedded IPv4 address NEED NOT be globally
unique; rather, it need only be topologically correct for (and unique
within) the context of
that the site.

This approach allows dual-stack nodes that do not share a common

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multiple access

datalink with an IPv6 gateway to join the global IPv6 network by
automatically tunneling IPv6 messages through the IPv4 routing
infrastructure within the their site. Two methods for automatic discovery
of an off-link IPv6 gateway within the site for ISATAP address autoconfiguration are
provided. This approach allows large-scale intra-site deployment
without incur-
ring incurring aggregation scaling issues at the border gateways,
since only a single IPv6 address prefix is used for the entire site.
Finally, this approach supports intranets which use non-globally
unique IPv4 addresses, such as when private address allocations
[PRIVATE] and/or Network Address Translation [NAT] are used; even when multiple levels
of NAT occur within used.

2. Changes

Major changes from version -00 to version -01:

- Revised draft to require *different* /64 prefixs for ISATAP
addresses and native IPv6 addresses. Thus, a given site.

In node's ISATAP
interface is assigned a /64 prefix that is distinct from the following sections, we present our proposed IPv6-IPv4 compati-
bility address format in detail. We further discuss technical con-
siderations for
prefixes assigned to any other interfaces attached to the application
node - be they physical or logical interfaces. This approach
eliminates ISATAP-specific sending rules presented in earlier
draft versions.

- Changed sense of IPv6-IPv4 compatibility addresses 'u/l' bit in the ISATAP address interface
identifier to facilitate incremental deployment of IPv6 indicate "local scope", since ISATAP interface
identifiers are unique only within predominantly
IPv4-based Intranets.

2. Changes the scope of the ISATAP
prefix. (See section 4.)

Major changes from version 01 personal draft to NGTRANS WG version 02: -00:

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

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

3. IPv6-IPv4 Compatibility Address Format

In sections 3.1 and 3.2, we will motivate our proposed extensions Terminology

The terminology of
the existing IEEE OUI reserved by IANA [IPv6] applies to support IEEE EUI-64 this document. Additionally, the
following terms are used extensively throughout this document:

ISATAP prefix:
Any globally aggregatable 64-bit IPv6 routing prefix (whether from a
native IPv6 assigned numbers authority or from a special-purpose numbering
scheme such as [6BONE][6TO4]) reserved by a local network administrator

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specifically for ISATAP purposes. ISATAP prefixes are used to configure
ISATAP addresses ONLY; native IPv6 addresses SHOULD NOT be configured
using an ISATAP prefix.

ISATAP address:
An IPv6 address with an ISATAP prefix and having an IPv4 address
embedded in the interface identifier in the manner described in
section 4 below.

ISATAP pseudo-interface:
ISATAP encapsulation of IPv6 packets inside IPv4 packets occurs
at a point that is logically equivalent to an IPv6 interface,
with the link layer being the IPv4 unicast network. This point
is referred to as a pseudo-interface. An ISATAP pseudo-interface
is assigned an ISATAP address through address autoconfiguration.

ISATAP router:
An IPv6 router supporting an ISATAP pseudo-interface. It is normally
an interior router within an heterogeneous IPv6/IPv4 network.

ISATAP host:
An IPv6 host which has an ISATAP pseudo-interface.

4. ISATAP Address Format

In sections 4.1 and 4.2, we will motivate our proposed extensions of
the existing IEEE OUI reserved by IANA to support IEEE EUI-64 format
addresses. While these proposed extensions are necessary to intended support
our IPv6-IPv4 compatibility the
ISATAP address format, they also provide a flex-
ible flexible framework for
future IANA use. Therefore, we believe the exten-
sions extensions proposed in sections 3.1 4.1
and 3.2 4.2 may provide beneficial future use to the IANA beyond the scope of IPv6-IPv4 compatibility
ISATAP addresses. We present our IPv6-IPv4 compatibility the ISATAP address format pro-
posal itself in sections 3.3 and 3.4 sec-
tions 4.3 and conclude this section with some
notes on deployment considerations.

3.1. 4.4.

4.1. IEEE EUI-64 Interface Identifiers in IPv6 Addresses

IPv6 aggregatable global and local-use unicast addresses [ADDR]
include a 64-bit interface identifier in IEEE EUI-64 format [EUI64],

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which is specified as the concatenation of a 24-bit company_id value
(also known as the OUI) assigned by the IEEE Registration Authority
(IEEE/RAC) and a 40-bit extension identifier assigned by the organi-
zation owning address-
ing authority for that OUI. (Normally, the addressing authority is
the organization to which the IEEE EUI-64 has allocated the OUI). IEEE EUI-
64 interface identifiers are for-
matted formatted as follows:

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|0 1|1 3|3 4|4 6|
|0 5|6 1|2 7|8 3|
+----------------+----------------+----------------+----------------+
|ccccccugcccccccc|ccccccccmmmmmmmm|mmmmmmmmmmmmmmmm|mmmmmmmmmmmmmmmm|
+----------------+----------------+----------------+----------------+

Where 'c' are the company-specific bits of the OUI, 'u' is the
universal/local bit, 'g' is the individual/group bit and 'm' are the
extension identifier bits. (NOTE: [ADDR] specifies that the 'u' bit
is inverted from its normal sense in the IEEE context; therefore u=1
indicates global scope and u=0 indicates local scope).

In order to support encapsulation of legacy IEEE EUI-48 (24-bit)
extension identifier values, [EUI64] specifies that the first two
octets of the EUI-64 40-bit extension identifier (bits 24 through 39
of the EUI-64 address itself) SHALL BE 0xFFFE if the extension iden-
tifier encapsulates an EUI-48 value. [EUI64] further specifies that
the first two octets of the extension identifier SHALL NOT be 0xFFFF,
as
since this value is reserved by the IEEE/RAC. However, all other 40-bit 40-
bit extension identifier values are available for assignment by the
OUI addressing authority responsible for a given OUI.

3.2. authority.

4.2. An EUI-64 Interface Identifier Format for IANA

The IANA owns IEEE OUI: 0x00005E (also written as: 00-00-5E), 00-00-5E, and [IANA] specifies EUI-48 format
(24-bit) interface identifier assign-
ments assignments within that OUI. But,
[IANA] does not specify how these legacy EUI-48 assignments will be
written in EUI-64 format, nor does it specify a format for future
40-bit extension identifier assignments. We propose the following
format for EUI-64 addresses within IANA's OUI reservation:

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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; indicates how (TSE, TSD) are interpreted (1 octet)

TSE Type-Specific Extension (1 octet)

TSD Type-Specific Data (3 octets)

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And the following interpretations are defined 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 identif-
ier id
0xFF RESERVED by IEEE/RAC

Essentially, if TYPE=0xFE, TSE is treated as an extension of TSD. If
TYPE=0xFF, TSE is treated as an extension of TYPE. Other values for
TYPE (and hence, other interpretations of TSE, TSD) are reserved for
future IANA use. This format conforms to all requirements specified
in [EUI64] and supports encapsulation of EUI-48 interface identifiers
in the manner described by that document. For example, an existing
IANA EUI-48 format multicast address such as:

01-00-5E-01-02-03

would be written in the IANA EUI-64 format as:

01-00-5E-FF-FE-01-02-03

But, this proposed format also provides a special TYPE (0xFE) for
embedding IPv4 addresses within the IANA 40-bit extension identifier.

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This special TYPE forms the basis for our IPv6-IPv4 compatibility
aggregatable global unicast the ISATAP address format proposal as
described in the following sections.

3.3. IPv6-IPv4 Compatibility

4.3. ISATAP Address Construction

Using the proposed IANA-specific method for interface identifier con-
struction discussed in sections 3.1 4.1 and 3.2 4.2 (with TYPE=0xFE), and
with reference to [ADDR], we can construct IPv6-IPv4 compatibility
aggregatable global unicast addresses. Using this methodology, we
propose an IPv6 address format with embedded IPv4 ISATAP address in the
EUI-64 interface identifier. The following diagram shows the con-
struction: as fol-
lows:

| 3| 13 | 8 | 24 | 16 | 8 | 8 | 8 | 8 | 32 bits |
+--+-----+---+--------+--------+---+---+---+---+---+---+---+----+
|FP| TLA |RES| NLA | SLA | 0x| 0x| 0x| 0x| IPv4 Address |
| | ID | | ID | ID | 02| 00| 00| 5E| FE| of Endpoint |
+--+-----+---+--------+--------+--------------------------------+

(NOTE: since ISATAP address interface identifiers are interpreted

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only within the local scope of the /64 ISATAP prefix, we set the u/l
bit in the least significant octet of the OUI in the interface iden-
tifier is 0x02 instead of 0x00 since u=1 for global to '0' to indicate
local scope.)

By way of example, an existing node with IPv4 address 140.173.129.8
might be assigned an IPv6 64-bit prefix of 3FFE:1a05:510:200::/64. We
can then construct an IPv6-IPv4 compatibility aggregatable global
unicast ISATAP address for this node as:

3FFE:1a05:510:200:0200:5EFE:8CAD:8108

3FFE:1a05:510:200:0:5EFE:8CAD:8108

or (perhaps more appropriately) written as the alternative form for
an IPv6 address with embedded IPv4 address found in [ADDR]:

3FFE:1a05:510:200:0200:5EFE:140.173.129.8

3FFE:1a05:510:200:0:5EFE:140.173.129.8

Similarly, we can construct the link-local and site-local variants
(respectively) of the IPv6-IPv4 compatibility ISATAP address as:

FE80::0200:5EFE:140.173.129.8
FEC0::200:0200:5EFE:140.173.129.8

3.4.

FE80::0:5EFE:140.173.129.8
FEC0::200:0:5EFE:140.173.129.8

4.4. Advantages

By embedding an IPv4 address in the interface identifier portion of
an IPv6 address as described in section 3.3, 4.3, we can construct aggre-
gatable global unicast IPv6 addresses that can either be routed

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globally glo-
bally via the IPv6 infrastructure or automatically tunneled locally
across portions of a site's IPv4 infrastructure which have no native
IPv6 routing support. Thus the addressing scheme supports
heterogeneous IPv6/IPv4 infrastructures in transition with incremen-
tal deployment of IPv6 at the site level. Additionally, a node with
such an IPv6-IPv4 compatibility ISATAP address could act
as a gateway for nodes with native IPv6 addresses connected to the same with which it
shares a common physical link, since it the ISATAP node could automatically automati-
cally tunnel messages across a site's IPv4 domain to
reach a border IPv6 gateway for the site on behalf of such the
native IPv6 nodes. An example would be deployment of IPv6 on some
subset of the hosts attached to a workgroup's Ethernet LAN. In this case, one
host would receive could configure an IPv6-IPv4 compatibility ISATAP address and act as a gateway for the other
hosts on the LAN which receive use native IPv6 addresses.

An additional advantage for our proposed method of embedding an IPv4
address in the interface identifier portion of an IPv6 address not
found in other approaches such as [6TO4] is that large numbers of
IPv6-IPv4 compatibility
ISATAP addresses could be assigned within a common IPv6 routing prefix, pre-
fix, thus providing maximal aggregation at the border gateways. For
example, the single 64-bit IPv6 prefix:

3FFE:1a05:510:2412::/64

could include literally millions of nodes with IPv6-IPv4 compatibil-
ity ISATAP addresses.

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This feature would allow a "sparse mode" IPv6 deploy-
ment deployment such as the
deployment of sparse populations of IPv6 hosts on large numbers of
independent links throughout a large corporate Intranet.

A final important advantage is that this method supports both sites
that use globally unique IPv4 address assignments and those that use
non-globally unique IPv4 addresses, such as when private address
assignments and/or Network Address Translation are used. By way of
analogy to the US Postal system, inter-domain transition approaches
such as [6TO4] provide means for routing messages "cross-country" to
the "street address" of a distant site while the approach outlined in
this document provides localized routing information to reach a
specific (mailstop, apartment number, post office box, etc) WITHIN
that site. Thus, the site-level routing information need not have
relevance outside the scope of that site.

3.5.

5. ISATAP Deployment Considerations

IPv6-IPv4 compatibility

ISATAP addresses should only be used by nodes which do not share a
common multiple access datalink with an a native IPv6 router. At least one ISATAP router
for their site. But, there are numerous cases in which such "iso-
lated" nodes may occur
must be configured within the site which advertises an heterogeneous IPv6/IPv4 Intranet.

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Two such examples are:

- A researcher wishes
administratively- assigned ISATAP prefix in response to run IPv6 on his existing IPv4-based works-
tation. One or more IPv6 routers are configured within the
researchers site, but the network administrators have not yet con-
figured an IPv6 router for the LAN that connects the researcher's
workstation.

- A network administrator within a large corporate network wishes
to configure IPv6 on the existing IPv4 subnets under their jurisd-
iction, but these subnets are separated Rtsol mes-
sage from an off-link host. Such off-link hosts will configure an
ISATAP pseudo-interface and assign it an address using the IPv6 border gate-
way for the corporation by other IPv4 subnets which are not ready
for IPv6 deployment.

In both examples, intra-site IPv6-in-IPv4 tunneling can be used to
span the "gaps" ISATAP
prefix it receives in IPv6 coverage. The IPv6-IPv4 compatibility an Rtadv message solicited from an ISATAP
router.

Following ISATAP address
format described in the previous subsections provides a means for
isolated nodes to configuration, ISATAP hosts automatically
and transparently communicate the IPv4 address of their *own* end of
the ISATAP tunnel to an off-link IPv6
gateway. any ISATAP host or router which uses the same
ISATAP prefix. While such nodes may optionally use stateful configuration
to set an ISATAP prefix and a "default" route that points to the off-link gateway, an ISA-
TAP router, a greatly preferred alternative is to provide for
automatic intra-site IPv6 router discovery and stateless address
autoconfiguration [DIS-
CUSS]. [DISCUSS]. The following section presents a means
for the automatic discovery of off-link IPv6 ISATAP routers.

5.1. Automatic Discovery of Off-link IPv6 ISATAP Routers

As described in [AUTO], a node that does not share a common multiple
access datalink with an IPv6 router will NOT receive unsolicited
Router Advertisements (Rtadv's), nor will Router Solicitations
(Rtsol's) from that node reach an IPv6 router on the local link. But,
the node may still be able to connect to the global IPv6 Internet if
an ISATAP router for the site exists. Hence, a means for off-link IPv6 ISATAP
router discovery is required. We present the following procedure for

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a node to initiate off-link IPv6 ISATAP router discovery (and for an off-link IPv6 ISATAP router
to respond) when
IPv6-IPv4 compatibility addresses are used:

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- The node constructs an IPv6-IPv4 compatibility ISATAP link local address for itself
(as described in section 3.) 4.) as:

FE80::0200:5EFE:V4ADDR_NODE

FE80::0:5EFE:V4ADDR_NODE

- The node discovers the IPv4 address for an off-link IPv6 ISATAP router
as: V4ADDR_RTR (**)

- The node sends an Rtsol to the IPv6 "all-routers-multicast" address
tunneled through the IPv4 infrastructure to the off-link IPv6 ISATAP router's
IPv4 address. The addresses used in the IPv6 and IPv4 headers are:

ipv6_src: FE80::0200:5EFE:V4ADDR_NODE FE80::0:5EFE:V4ADDR_NODE
ipv6_dst: FF02::2
ipv4_src: V4ADDR_NODE
ipv4_dst: V4ADDR_RTR

- Upon receiving the tunneled Rtsol, the off-link IPv6 ISATAP router sends
a unicast Rtadv to the unicast address of the node which sent the
Rtsol; again, by tunneling the Rtadv through IPv4. The addresses
used in the IPv6 and IPv4 headers are:

ipv6_src: FE80::0200:5EFE:V4ADDR_RTR FE80::0:5EFE:V4ADDR_RTR
ipv6_dst: FE80::0200:5EFE:V4ADDR_NODE FE80::0:5EFE:V4ADDR_NODE
ipv4_src: V4ADDR_RTR
ipv4_dst: V4ADDR_NODE

- Upon receiving the Rtsol, the originating node performs address
autoconfiguration as described in [AUTO] and constructs:

- a fully-qualified IPv6-IPv4 compatibility ISATAP address for use as the source address
for IPv6 packets an ISATAP pseudo-interface

- a default route that points to the off-link IPv6 router's
IPv6-IPv4 compatibility link-local address ISATAP router

Note (**) that the above procedure assumes a means for discovering
V4ADDR_RTR. We present two alternative methods for the automatic
discovery of V4ADDR_RTR:

4.1.

5.2. DNS Well-Known Service Name

The first method for discovering V4ADDR_RTR employs a new DNS Well-
Known Service (WKS) name [DNS1,DNS2]. With the establishment of a new

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well-known service name (e.g. "V6V4GW"), "ISATAPGW"), administrators could publish pub-
lish the IPv4 address of a gateway which implementations could use to

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discover V4ADDR_RTR. This method has the advantage that it can be
deployed immediately using existing mechanisms. However, it requires
name service lookups and may not always provide the optimum
V4ADDR_RTR resolution for isolated hosts which use IPv6-IPv4 compati-
bility addresses.

4.2. if multiple ISATAP routers
are available.

5.3. IPv4 Anycast for Intra-domain IPv6 router ISATAP routers

[6TO4ANY] proposes an IPv4 anycast prefix for 6to4 relay routers.
The proposal suggests an IPv4 prefix assignment 'x.x.x.0/nn' ('nn' is
currently proposed as 16) where the single address 'x.x.x.1' is
assigned as the "6to4 IPv6 relay anycast address". We propose analo-
gous assignments for the purpose of an "IPv6-IPv4 compatibility "ISATAP router anycast
address". (Whether the reservation of a second /32 assignment from
the 6to4 IPv4 anycast prefix proposed in [6TO4ANY] would be possible,
or a separate prefix assignment would be required is a matter of
debate and TBD.)

Any IPv6 router capable of providing an IPv6-IPv4 compatibility
address-based tunnel endpoint as described in the previous sections

ISATAP routers would advertise the IPv6-IPv4 compatibility ISATAP router anycast prefix via
the intra-domain IPv4 routing infrastructure. Isolated IPv6 nodes
would then use the IPv6-IPv4 compatibility ISATAP router anycast address as the V4ADDR_RTR
IPv4 destination for off-link Rtsol's. This approach has the significant signifi-
cant advantages that:

- implementations could hard-code the well-known V6V4Compat ISATAP
anycast address, thus avoiding service discovery via DNS

- an optimum path to an off-link IPv6 ISATAP router would be ensured
by intra-domain IPv4 routing

As described above, the IPv4 anycast method for locating intra-domain ISATAP
routers that support IPv6-IPv4 compatibility address-based tunneling provides significant functional advantages over the DNS
approach, while the DNS approach can be implemented immediately pending pend-
ing the registration of a WKS name with IANA. While either method
will work, the decision of which to push for standardization is TBD
pending dis-
cussion discussion at upcoming NGTRANS WG meetings.

6. Sending Rules and Routing Considerations

The sending rule for a host or router that sends an IPv6 packet to

Since each node will be assigned an
IPv6-IPv4 compatibility destination address ISATAP prefix which is simple and direct:

"If the 64-bit IPv6 adminis-
tratively reserved for use ONLY by ISATAP nodes, no special sending
rules are needed. In particular, correspondent nodes that share a
common ISATAP prefix of the IPv6-IPv4 compatibility will always exchange messages using their ISATAP
pseudo-interfaces, whereas nodes that do not share a common ISATAP

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destination address matches the 64-bit IPv6

prefix of one of my
network interfaces, tunnel the packet through IPv4 - else, route
the packet through IPv6."

From the above rule, will always exchange messages via standard IPv6 routing. When
sending a sender that does NOT have message on an interface which
shares a common 64-bit routing prefix with ISATAP pseudo-interface, an implementation
SHOULD verify that the packet's IPv6-IPv4
compatibility IPv6 destination address simply sends employs the packet ISATAP
address construction rules described in section 4 in order to the
next-hop gateway determined detect
mis-configured addresses. No other sending rules are necessary.

7. Address Selection

No special address selection rules are necessary.

8. Automatic Deprecation

ISATAP addresses are intended for use only by an ordinary nodes which do not
receive native IPv6 routing table lookup.
In short, when a sending node does Rtadv's due to not have an interface which shares sharing a common 64-bit (site-level) routing prefix datalink with
an IPv6-IPv4 compa-
tibility destination address, the sending rule is identical to that
for a IPv6 router. When native IPv6 destination address. This decision is independent
of whether the sender has Rtadv's become available (such as
when an IPv6-IPv4 compatibility address itself,
or whether the sender even comprises IPv6 router is deployed on a dual-stack configuration.
Indeed, node's datalink), the sender can simply be a native IPv6 node with no legacy
IPv4 support.

When
should construct a sender has an interface which shares a common 64-bit routing
prefix with an IPv6-IPv4 compatibility destination address, however,
the sender must assume that the destination is NOT directly reachable
at the datalink level - even though the shared site-level routing
prefix implies otherwise. Instead, if the sender comprises a dual-
stack configuration, it should automatically tunnel the IPv6 packet
(via IPv6-in-IPv4 tunneling as described in [MECH]) to the IPv4
address embedded within the IPv6-IPv4 compatibility destination
address' interface identifier. If the sender is an IPv6-only node
that DOES NOT comprise a dual-stack configuration, however, it has no
means for automatically tunneling the packet via IPv4. In this case:

- If the sender is the host that originates the packet, it should
send the packet to a router that lists the 64-bit prefix in its
router advertisements. If no such router exists, the sender should
drop the packet and return a "No route to host" error indication
to the originating application.

- If the sender is a router that forwards the packet, it should drop
the packet and send an ICMPv6 "Destination Unreachable" message to
the source

By implication, the scheme breaks down if a packet with an IPv6-IPv4
compatibility destination address reaches an IPv6-only router that
has an interface which shares a common 64-bit routing prefix with the
destination address. Additional mechanisms to address this issue
might be possible, such as allowing dual-stack routers to advertise
96-bit prefixes which incorporate the special 32-bit EUI-64 interface
identifier prefix: 0200:5EFE. A sender could then interpret such an
advertisement to mean that the advertising router comprises a dual
stack and is capable of intra-site IPv6-in-IPv4 tunneling. But a

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reasonable argument could be made to the effect that:

"By the time IPv6-only routers begin to proliferate throughout a
site, nodes within the site should no longer be using IPv6-IPv4
compatibility addresses."

In fact, the advent of IPv6-only routers within a site would serve as
a strong indication that the site is no longer a predominantly IPv4-
based infrastructure in transition, but rather that the transition is
either complete or nearly complete. Therefore, IPv6-IPv4 compatibil-
ity addresses should no longer be used.

6. Address Selection

Other works in progress ([6TO4] and [SELECT]) have begun to explore
the subject of address selection when multiple IPv6 destination
address alternatives are available. These address selection policies
deal with the 64-bit IPv6 routing prefix and thus can be applied
independently of whether/not the destination address alternatives are
constructed as described in this document. However, in order to
ensure efficient routing within the destination's site, we propose
the following simple "second-tier" address selection policy for deal-
ing with IPv6-IPv4 compatibility addresses:

"If multiple alternatives remain after address selection has been
applied on the 64-bit routing prefixes, and if at least one of the
remaining alternatives is constructed with a native IPv6 interface
identifier (one that does NOT contain an embedded IPv4 address as
described in this document), select a native IPv6 address. Other-
wise, select an IPv6-IPv4 compatible address."

This policy decision is in keeping with the concept that NGTRANS
transition mechanisms should remain in place ONLY as long as needed
and should be disabled as soon as native IPv6 mechanisms become
available.

7. Automatic Deprecation

IPv6-IPv4 compatibility addresses constructed in the manner described
in this document are intended for use only by nodes which do not
receive router advertisements due to not sharing a common multiple
access datalink with an IPv6 router. When router advertisements
become available (such as when an IPv6 router is deployed on a common
multiple access datalink shared by the node), the node should discon-
tinue use of its IPv6-IPv4 compatibility address and adopt a normal non-ISATAP aggregatable global IPv4 IPv6 unicast
address using address auto-

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configuration auto-configuration [AUTO] for a non-ISATAP IPv6
prefix discovered through normal router
discovery [DISC] means. In this way, IPv6-IPv4 compatibility
addresses will gradually (and automatically) disappear as means [DISC]. After the node's
native IPv6
routers become widely deployed within a site.

8. Multicast Considerations

Other works in progress are currently investigating IPv4-mapped mul-
ticast addressing issues. The address format discussed in this docu-
ment is expected to be compatible with those emerging approaches.

9. Relation to other works in progress

The IPv6-IPv4 compatibility address format and routing policy deci-
sions presented populated in this draft evolved from SRI contractual works out-
side the scope of the NGTRANS working group. Additionally, the
mechanisms presented in this draft were developed by DNS, the author with
no prior knowledge of node should eventu-
ally cease sending Rtsol's to the activities in NGTRANS. The author recog-
nizes that other ISATAP router and discontinue use
of its ISATAP pseudo-interface. In this way, ISATAP addresses will
gradually (and automatically) disappear as IPv6 routers are widely
deployed within sites.

9. Multicast Considerations

Other works in progress seek to address very similar
IPv4-IPv6 transition [6TO4MULTI] are currently investigating mul-
ticast addressing issues as those targeted by this draft. However,
the approach described in this draft presents a number of unique
advantages for NGTRANS that supplement the other works [6TO4]. The address format discussed in progress.
(Most specifically, advantages for incremental deployment of IPv6
nodes at the intra-domain level.)
this document is expected to be compatible with those emerging
approaches.

10. IANA considerations

In order to support the EUI-64 address form described in this docu-
ment, we propose that IANA adopt the EUI-64 Interface Identifier for-
mat specified in section 3.2 4.2 for the existing 00-00-5E OUI owned by
IANA. No other actions are required by the IANA.

11. Security considerations

The IPv6-IPv4 compatibility ISATAP address format does not support privacy extensions for
stateless address autoconfiguration [PRIVACY]. How-
ever, However, such privacy

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extensions are intended primarily to avoid reveal-
ing revealing one's MAC
address, and the IPv6-IPv4 compatibility ISATAP address format described in this document
accomplishes this same goal.

Additional security issues are called out in [6TO4] and probably
apply here as well.

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12. Implementation status

The author has implemented the mechanisms described in this draft
through modifications to the FreeBSD 3.2-RELEASE [FBSD] operating
system with the INRIA [INRIA] IPv6 distribution. These modifications
implement the sending rules and routing considerations as described
in section 5. The source code A Linux implementa-
tion is not yet ready planned for public distribu-
tion, but the author would be happy to discuss details with
interested parties. June, 2001 timeframe.

Additionally, Windows XP RC1 will implement elements of the mechanism
proposed in this paper.

Acknowledgements

The original ideas presented in this draft were derived from SRI contractual con-
tractual work. The author recognizes that ideas similar to those in
this document may have already been presented by others and wishes to ack-
nowledge
acknowledge any other such authors. The author also wishes to ack-
nowledge the government contract administrators who sponsored the
projects from which these works derived as well as his SRI colleagues
with whom he has discussed and reviewed this work, including Monica
Farah-Stapleton, Dr. Mike Frankel, J. Peter Marcotullio, Lou Rodriguez, Rodri-
guez, and Dr. Ambatipudi Sas-
try. Sastry.

The author acknowledges discussions with Alain Durand and Keith Moore
during valuable input from numerous members of the IETF 48 conference in Pittsburgh, PA.
NGTRANS community which has helped
motivate ideas on restructuring this document guide the direction of the draft.
The list of contributors is too long to enumerate, but the input from
the first version. community has been vital to the draft's evolution. Alain Durand
deserves special mention for contributing the title of this draft and
the ISATAP acronym.

The author further finally wishes to provide special acknowledgement to Dave
Thaler, Art Shelest, Richard Draves, and their colleagues others at Microsoft Research
for their ideas on automatic discovery of off-link IPv6 routers. Much
of the text in that section on deployment considerations derives directly
from discussions with Dave,
Art Art, Rich and others.

References

[AGGR] Hinden., R, O'Dell, M., and Deering, S., "An IPv6
Aggregatable Global Unicast Address Format",
RFC 2374, July 1998.

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[ADDR] Hinden, R., and S. Deering, "IP Version 6 Addressing
Architecture", RFC 2373, July 1998.

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

[DISC] Narten, T., Nordmark, E., and W. Simpson, "Neighbor

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Discovery for IP Version 6 (IPv6)", RFC 2461,
December 1998.

[DNS1] Mockapetris, P. "Domain names - concepts and facilities",
STD 13, RFC 1034, November 1987.

[DNS2] Mockapetris, P. "Domain names - Implementation and Specif-
ication",
STD 13, RFC 1035, November 1987.

[DNSSRV] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782,
February 2000.

[EUI64] IEEE, "Guidelines for 64-bit Global Identifier (EUI-64)
Registration Authority",
http://standards.ieee.org/regauth/oui/tutorials/EUI64.html,
March 1997

[IANA] Reynolds, J., and J. Postel, "Assigned Numbers", STD 2,
USC/Information Sciences Institute, October 1994.

[IPV4] Postel, J., "Internet Protocol", RFC 791

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

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

[6TO4ANY] Huitema, C., "An anycast prefix for 6to4 relay routers",
draft-ietf-ngtrans-6to4anycsat-02.txt (work in progress)

[6TO4MULTI] Thaler, D., "Support for Multicsat over 6to4 Networks",
draft-ietf-ngtrans-6to4-multicast-00.txt (work in pro-
gress)

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

[SELECT] Draves, R., Default Address Selection for IPv6, draft-

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ietf-
ipngwg-default-addr-select-00.txt (work in progress)

[FBSD] http://www.freebsd.org

[INRIA] ftp://ftp.inria.fr/network/ipv6/

[6BONE] Rockell, R., and R. Fink, RFC 2772, February 2000.

[PRIVATE] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.
J.,

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and E. Lear, "Address Allocation for Private Internets",
RFC 1918, February 1996.

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

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

[DISCUSS] private discussions with Dave Thaler, Art Shelest, et al.

Authors Addresses

Fred L. Templin
SRI International
333 Ravenswood Ave.
Menlo Park, CA 94025, USA

Email: templin@erg.sri.com

Intellectual Property

PLACEHOLDER for full IETF IPR Statement if needed.

Full Copyright Statement

PLACEHOLDER for full ISOC copyright Statement if needed.

Templin Expires 12 October 17 November 2001 [Page 16] 14]

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