wdiff draft-ietf-ngtrans-isatap-02.txt draft-ietf-ngtrans-isatap-03.txt

NGTRANS Working Group Fred L. F. Templin
INTERNET-DRAFT SRI International
T. Gleeson
Cisco Systems K.K.
M. Talwar
D. Thaler
Microsoft Corporation

Expires 21 May 2001 21 November 2001 30 July 2002 30 January 2002

Intra-Site Automatic Tunnel Addressing Protocol (ISATAP)

draft-ietf-ngtrans-isatap-02.txt

draft-ietf-ngtrans-isatap-03.txt

Abstract

This document specifies an intra-site automatic tunneling protocol the Intra-Site Automatic Tunnel Addressing
Protocol (ISATAP) for connecting that connects IPv6 hosts and routers (nodes) within
predominantly IPv4-based networks. This method is based on an IPv6
aggregatable global unicast address format (described herein) that
embeds the
IPv4 address of sites. ISATAP is a node within the EUI-64 format interface
identifier. This document assumes that, during the IPv4 to IPv6 co-
existence and transition phase, many sites will deploy mechanism that enables incremental
deployment of IPv6
incrementally within their IPv4 interior routing domains; especially
those sites which have large and complex pre-existing IPv4
infrastructures. Within such sites, by treating the address format and methods
described in this document will enable IPv6 deployment for nodes that
do not share site's IPv4 infrastructure as a common
Non-Broadcast Multiple Access (NBMA) link with an IPv6 gateway for their site.

While other works in progress in the NGTRANS working group propose layer. ISATAP mechanisms for assigning globally-unique
use a new IPv6 interface identifier format that embeds an IPv4
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 automatic IPv6-in-IPv4 tunneling within a site's pre-existing IPv4
infrastructure without incurring aggregation scaling issues at
site, whether the
border gateways nor requiring site-wide deployment of special site uses globally assigned or private IPv4
services such as multicast.
addresses. The approach proposed by new interface identifier format can be used with both
local and global unicast IPv6 prefixes - this document
supports enables IPv6 routing within
both the site-local locally and global IPv6 globally. ISATAP mechanisms introduce no impact on
routing domains as well as automatic IPv6 in IPv4 tunneling across
portions of a site's IPv4 infrastructure which have table size and require no native IPv6
support. Additionally, this approach supports automatic tunneling
within sites which use non globally-unique special IPv4 address assignments,
such as when Network Address Translation [NAT] is used. services (e.g., IPv4
multicast).

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
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 using
the existing global IPv4 backbone as transit. But, these islands may
themselves comprise complex heterogeneous IPv4/IPv6 networks (e.g.
large academic or commercial campus intranets) that require intra-
domain IPv4 to IPv6 transition mechanisms and strategies as well. In
order to address this requirement, this

This document presents a simple
and simple, scalable approach that enables
incremental deployment of IPv6
nodes within predominantly IPv4-based intranets. sites in a manner
that is compatible with inter-domain transition mechanisms, e.g.,
[6TO4]. We refer to this approach as the Intra-Site Automatic Tunnel
Addressing Protocol, or ISATAP (pronounced: "ice-a-tap"). ISATAP is based on 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 Interface Identifier [EUI64].
This address format is fully compatible with both native IPv6 and
NGTRANS routing practices (e.g. [6to4],[6BONE]). But, the interface
identifier in an ISATAP address employs a special construction that
encapsulates an IPv4 address suitable for automatic IPv6-in-IPv4 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 the site.

ISATAP
allows dual-stack nodes that do not share a common link with an IPv6 gateway
router to join the global IPv6 network by automatically tun-
neling tunnel packets to the IPv6 messages next-hop address
through IPv4, i.e., the site's IPv4 routing infrastructure within
their site. Two methods is treated as an
NBMA link layer.

This document specifies details for automatic discovery the transmission of an IPv6 gateway
for packets
over ISATAP address autoconfiguration are provided. This approach
allows large-scale intra-site deployment without incurring aggrega-
tion scaling issues at border gateways, since only links (i.e., automatic IPv6-in-IPv4 tunneling), including
a single global
IPv6 new EUI-64 [EUI64] based interface identifier [ADDR][AGGR] format
that embeds an IPv4 address. This format supports configuration of
global, site-local and link-local addresses as specified in [AUTO] as
well as simple link-layer address prefix need be used mapping. Simple validity checks for
received packets are given. Also specified in this document is the entire site. (Multiple pre-
fixes are, however, supported and may be used
operation of IPv6 Neighbor Discovery for site renumbering
and simliar purposes.) Finally, this approach supports networks which
use non-globally unique IPv4 addresses, such ISATAP, as when private address
allocations permitted for
NBMA links by [DISC]. The document finally presents deployment and
security considerations for ISATAP.

2. Applicability Statement

ISATAP provides the following features:

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

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

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

- supports both stateless address autoconfiguration and manual
configuration
- supports networks that use non-globally unique IPv4 addresses (e.g.,
when private address allocations [PRIVATE] and/or are used), but does not
allow the virtual ISATAP link to span a Network Address Translation
Translator [NAT] are
used.

2. Changes

Major changes from version 01 to version 02:

- Cleaned up text and tightened up terminology. Changed "IPv6 destination
address" to "IPv6 next-hop address" under "sending rules". Changed
definition compatible with other NGTRANS mechanisms (e.g., [6TO4])

3. Terminology

The terminology of ISATAP prefix [IPv6] applies to include this document. The following
additional terms are defined:

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

underlying link:
a link layer that supports IPv4 (for ISATAP), and site-local. Changed
language in sections 4 and 5

- Updated status of Linux implementation

Major changes from version 00 to version 01:

- Revised draft to require *different* /64 prefixs for MAY also support
IPv6 natively.

ISATAP link:
one or more underlying links used for IPv4 tunneling. The IPv4
network layer addresses and native IPv6 addresses. Thus, of the underlying links are used as
link-layer addresses on the ISATAP link.

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

ISATAP prefix:
a /64 prefix that is distinct from used to configure an address on the
prefixes ISATAP interface. This
prefix is administratively assigned to any other interfaces attached to the
node - ISATAP link and MUST NOT
be they physical or logical interfaces. This approach
eliminates ISATAP-specific sending rules presented in earlier
draft versions.

- 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.)

Major changes from personal draft to version 00:

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

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

3. Terminology

The terminology of [IPv6] applies to this document. Additionally, the
following terms are used extensively throughout this document:

ISATAP prefix:
Any link-local, site-local or globally aggregatable IPv6 prefix declared
as such. An ISATAP prefix configures ONLY ISATAP addresses within its
scope; native IPv6 addresses SHOULD NOT be configured on an ISATAP prefix. links.

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

Native IPv6 address:
An IPv6 address constructed using a non-ISATAP prefix.

ISATAP pseudo-interface: 4.

ISATAP encapsulation of router:
an IPv6 packets inside IPv4 packets occurs
at a point node that is logically equivalent to has an IPv6 interface,
with the link layer being the IPv4 unicast network. This point
is referred ISATAP interface over which it forwards
packets not explicitly addressed to as a pseudo-interface. An itself.

ISATAP pseudo-interface
is assigned host:
any node that has an ISATAP address through address autoconfiguration. interface and is not an ISATAP router:
An router.

4. Transmission of IPv6 router supporting an Packets on ISATAP pseudo-interface. It is normally
an interior router within an heterogeneous IPv6/IPv4 network. Links

ISATAP host:
An links transmit IPv6 host which has packets via automatic tunneling using the
site's IPv4 infrastructure as an NBMA link layer. Automatic tunneling
for ISATAP pseudo-interface.

4. ISATAP Address Format

In uses the following sections, we will motivate our proposed extensions
of the existing IEEE OUI reserved by the Internet Assigned Numbers
Authority [IANA] to support IEEE EUI-64 format addresses as well as same mechanisms specified in [MECH,3.1-3.6],
i.e., IPv6 packets are automatically encapsulated in IPv4 using 'ip-
protocol-41' as the payload type number. Specific considerations for
ISATAP address format itself. links are given below:

4.1. IEEE EUI-64 ISATAP Interface Identifiers in IPv6 Addresses Identifier Construction

IPv6 aggregatable global and local-use unicast addresses [ADDR] [ADDR][AGGR] include a 64-bit interface identifier iden-
tifier field in "modified EUI-64 format", based on the IEEE EUI-64
[EUI64] specification. (Modified EUI-64 format [EUI64],
which is specified as inverts the concatenation sense of a 24-bit company_id value
(also known as
the OUI) assigned by 'u/l' bit from its specification in [EUI64], i.e., 'u/l' = 0
indicates local-use.) ISATAP specifies an [EUI64]-format address con-
struction for the IEEE Registration Authority
(IEEE/RAC) and a 40-bit extension identifier assigned Organizationally-Unique Identifier (OUI) owned by
the address-
ing authority for that OUI. (Normally, the addressing authority Internet Assigned Numbers Authority [IANA]. This format (given
below) is
the organization used to which the IEEE has allocated the OUI). IEEE EUI-
64 construct both native [EUI64] addresses for general
use and modified EUI-64 format interface identifiers are formatted as follows: for use in IPv6
unicast addresses:

|0 1|1 2|2 3|3 4|4 3|4 6|
|0 5|6 3|4 1|2 7|8 9|0 3|
+----------------+----------------+----------------+----------------+
|ccccccugcccccccc|ccccccccmmmmmmmm|mmmmmmmmmmmmmmmm|mmmmmmmmmmmmmmmm|
+----------------+----------------+----------------+----------------+
+------------------------+--------+--------+------------------------+
| OUI ("00-00-5E"+u+g) | TYPE | TSE | TSD |
+------------------------+--------+--------+------------------------+

Where 'c' are the company-specific 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 OUI, 'u' 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 the
universal/local bit, 'g' 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

Thus, if TYPE=0xFE, TSE is the individual/group bit and 'm' are the an extension identifier bits. (NOTE: [ADDR] specifies that the 'u' bit of TSD. If TYPE=0xFF, TSE 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)
an extension identifier values, [EUI64] specifies that the first two
octets of the EUI-64 40-bit extension identifier (bits 24 through 39 TYPE. Other values for TYPE (hence, other interpreta-
tions of the EUI-64 TSE, TSD) are reserved for future IANA use.

The above specification is compatible with all aspects of [EUI64],
including support for encapsulating legacy EUI-48 interface identif-
iers (e.g., an IANA EUI-48 format multicast address itself) SHALL BE 0xFFFE if such as: '01-00-
5E-01-02-03' is encapsulated as: '01-00-5E-FF-FE-01-02-03'). But, the extension iden-
tifier encapsulates
specification also provides a special TYPE (0xFE) to indicate an EUI-48 value. [EUI64] further specifies that IPv4
address is embedded. Thus, when the first two four octets of the extension a [ADDR]-
compatible IPv6 interface identifier SHALL NOT be 0xFFFF,
since this value is reserved by are: '00-00-5E-FE' (note: the IEEE/RAC. However, all other 40-
'u/l' bit extension identifier values are available for assignment by MUST be 0) the
OUI addressing authority.

4.2. An EUI-64 Interface Identifier Format for IANA

The IANA owns IEEE OUI: 00-00-5E, and [IANA] specifies EUI-48 format
(24-bit) interface identifier assignments within that OUI. But,
[IANA] does not specify how these legacy EUI-48 assignments will is said to be
written in EUI-64 format, nor does it specify a format for future
40-bit extension identifier assignments. We propose "ISA-
TAP format" and the following
format for EUI-64 next four octets embed an IPv4 address encoded in
network byte order (least significant octet first). Addresses con-
figured on the ISATAP interface MUST use the ISATAP interface iden-
tifier format.

4.2. Stateless Autoconfiguration and Link-Local Addresses

ISATAP addresses within IANA's OUI reservation:

|0 2|2 3|3 3|4 6|
|0 3|4 1|2 9|0 3|
+------------------------+--------+--------+------------------------+ are unicast addresses [ADDR,2.5] that use ISATAP
format interface identifiers as follows:

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)

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 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.
This special TYPE forms the basis for the ISATAP address format as
described in the following sections.

4.3. ISATAP Address Construction

Using the proposed IANA-specific method for interface identifier con-
struction discussed in sections 4.1 and 4.2 (with TYPE=0xFE), and
with reference to [ADDR], we can construct an ISATAP address as fol-
lows:

| 3| 13 | 8 | 24 | 16 | 8 | 8 | 8 | 8 | 32 bits |
+--+-----+---+--------+--------+---+---+---+---+---+---+---+----+
|FP| TLA |RES| NLA link-local, site-local or | SLA 0000:5EFE | 0x| 0x| 0x| 0x| IPv4 Address |
| global unicast prefix | ID | | ID | ID | 00| 00| 5E| FE| of Endpoint |
+--+-----+---+--------+--------+--------------------------------+

(NOTE: since ISATAP address interface identifiers are interpreted
only within the local scope of the /64 ISATAP prefix, we set the u/l
bit in the least significant octet of the OUI 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 ISATAP address for this node as:

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

Similarly, we can construct the link-local link |
+------------------------------+---------------+----------------+

Link-local, site-local, and site-local variants
(respectively) of the ISATAP address as:

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 4.3, we can construct aggre-
gatable global unicast IPv6 ISATAP addresses that can either be routed glo-
bally via the IPv6 infrastructure can be created
exactly as specified in [ADDR], (e.g., by auto-configuration [AUTO]
or automatically tunneled locally
across portions of a site's IPv4 infrastructure which have no native manual configuration). For example, the IPv6 support. Additionally, address:

3FFE:1a05:510:1111:0:5EFE:8CAD:8108

has a node with both prefix of '3FFE:1a05:510:1111::/64' and an ISATAP link format inter-
face 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

The link-local and a
native IPv6 link could act as a router for nodes that share its
native link, since the site-local variants (respectively) are:

FE80::0:5EFE:140.173.129.8
FEC0::1111:0:5EFE:140.173.129.8

4.3. ISATAP Link/Interface Configuration

A node could automatically tunnel mes-
sages across a site's configures an ISATAP link over one or more underlying IPv4 domain on behalf of
links, i.e., the native IPv6 nodes.
An example would ISATAP link MAY be deployment of IPv6 on a workgroup LAN. In this
case, configured over one host could or more
link-layer (IPv4) addresses. Each link-layer address 'V4ADDR_LINK' is
used to configure a link-local address 'FE80::0:5EFE:V4ADDR_LINK' on
an ISATAP address and act interface. ISATAP interfaces MAY be assigned one per link-
layer address, or as a router single interface for other hosts which use native IPv6 addresses on multiple link-layer
addresses.

In the LAN.

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

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

could include literally millions of nodes with latter case, the inter-
face will accept ISATAP addresses.
This feature would allow a "sparse mode" IPv6 deployment such 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 represented in the
deployment of sparse populations of Poten-
tial Routers List.

4.4. Sending Rules and Address Mapping

The IPv6 hosts next-hop address for packets sent on large numbers of
independent links throughout a large corporate Intranet.

A final important advantage is that this method supports both sites an ISATAP link MUST be
an ISATAP address. Packets that use globally unique IPv4 address assignments do not satisfy this constraint MUST
be discarded and those that use
non-globally unique IPv4 addresses, such as when private address
assignments and/or Network Address Translation an ICMP destination unreachable indication with code
3 (Address Unreachable) [ICMPv6] MUST be returned. No other sending
rules are used. By way of
analogy to the US Postal system, inter-domain transition approaches
such as [6TO4] provide means necessary.

The procedure for routing messages "cross-country" mapping unicast addresses into link-layer addresses
is to simply treat the "street address" last four octets 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.

5. ISATAP Deployment Considerations

Hosts should only use address as an
IPv4 address (in network byte order). No multicast address mappings
are specified.

4.5. Validity Checks for Received Packets

ISATAP on interfaces which MUST silently discard any received packets that do
not share a com-
mon link with satisfy ONE OF the following validity checks:

- the network-layer (IPv6) source address has a native IPv6 router. Routers may configure both prefix configured on
the ISATAP interface and Native IPv6 links on an ISATAP-format interface identifier that
embeds the same physical interface, but link-layer (IPv4) source address, i.e., source is on-link

- the pre-
fixes used will be distinct. An link-layer (IPv4) source address is in the Potential Routers List
(see section 5.2), i.e., previous hop is an on-link ISATAP router can

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 and next-hop determi-
nation should be configured implemented as described in this document. Address
resolution and the mechanism for delivering Router Solicitations
and Advertisements on
any NBMA links is not specified in this docu-
ment."

ISATAP link to advertise links SHOULD implement Redirect, Neighbor Unreachability
Detection, and next-hop determination exactly as specified in [DISC].
Address resolution and the prefix(es) administratively assigned
to 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 link. Since
these mechanisms MAY potentially apply to other types of NBMA links
in the future.)

5.1. Address Resolution

Protocol addresses (IPv6) in ISATAP is NBMA, these advertisements are not
periodically multicast resolved to link-layer
addresses (IPv4) by a static computation, i.e., the router, but last four octets
are solicited by Rtsols
sent by hosts. Hosts will configure treated as an ISATAP pseudo-interface and
assign it address(es) based on IPv4 address. Thus the ISATAP prefix(es) in functions and conceptual
data structures used by [DISC] for the solicited
Rtadv messages.

Following ISATAP purpose of address configuration, ISATAP hosts communicate resolution
are not required. The conceptual "neighbor cache" described in [DISC]
is still needed for other functions, such as
regular IPv6 peers. neighbor unreachability
detection, but it is not used for address resolution.

The source link-layer address of such packets will be option used in
ISATAP format. Replies sent to this [DISC] is not needed. Implemen-
tations SHOULD NOT send link-layer address can thus be automatically
tunneled over the last IPv6 hop, options in any Neighbor
Discovery packets, and MUST silently ignore any such options in
Neighbor Discovery packets which occurs on the ISATAP network.
While nodes may optionally use stateful configuration to set an ISA-
TAP prefix are received.

5.2. Router and a "default" route that points to an ISATAP router, a
greatly preferred alternative Prefix Discovery

Since the site's IPv4 infrastructure is to treated as an NBMA link
layer, unsolicited Router Advertisements do not provide for automatic intra-site
IPv6 router discovery and stateless address autoconfiguration [DIS-
CUSS]. The following section presents a sufficient
means for the automatic router discovery of on ISATAP routers.

5.1. Automatic Discovery of links. Thus, alternate mechan-
isms are required and specified below:

5.2.1. Conceptual Data Structures

ISATAP Routers

As described nodes use the Prefix List and Default Router List conceptual
data structures exactly as specified in [AUTO], a node that does not share [DISC,5.1]. ISATAP links add
a common link with
an IPv6 router will NOT receive unsolicited Router Advertisements
(Rtadv's), nor will new conceptual data structure "Potential 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 List" and the site exists. Hence, a means for ISATAP router discovery fol-
lowing new configuration variable:

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

A Potential Router List (PRL) is
required. We present the following procedure for a node to initiate associated with every ISATAP link.
The PRL provides context for router discovery (and 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. The
IPv4 address represents a router's ISATAP router interface (likely to respond) when be an
on-link IPv6 router
"advertising interface"), and is not available:

- The node constructs an used to construct the ISATAP link link-
local address for itself
(as described in section 4.) as:

FE80::0:5EFE:V4ADDR_NODE

- The node discovers that interface.

When the IPv4 address for an ISATAP router
as: V4ADDR_RTR (**)

- The node sends enables an Rtsol to ISATAP link, it initializes the IPv6 "all-routers-multicast" address
tunneled PRL with
IPv4 addresses discovered through name service lookups for the IPv4 infrastructure Well-
Known Service name "ISATAP" (see "IANA Considerations"). Nodes
periodically repeat this process after ResolveInterval to detect
additions/deletions for the ISATAP router's PRL. Initialization of the PRL through
static IPv4 address. The addresses used address assignments and/or an alternate name for lookups
is a supported configuration option, but the method described above
is preferred.

5.2.2. Validation of Router Advertisement Messages

A node MUST silently discard any received Router Advertisement mes-
sages that do not satisfy the validity checks in [DISC,6.1.2] as well
as the IPv6 and IPv4 headers are:

ipv6_src: FE80::0:5EFE:V4ADDR_NODE
ipv6_dst: FF02::2
ipv4_src: V4ADDR_NODE
ipv4_dst: V4ADDR_RTR following additional validity check for ISATAP:

- Upon receiving the tunneled Rtsol, network-layer (IPv6) source address is from the PRL

5.2.3. Router Specification

Advertising ISATAP interfaces of routers behave the same as advertis-
ing interfaces described in [DISC,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 sends receives a valid Router Solicitation on an
advertising ISATAP interface, it replies with a unicast Rtadv Router Adver-
tisement to the unicast address of the node which sent the
Rtsol; again, Router Solicita-
tion. 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.

By default, ISATAP routers will not receive Router Advertisements
from other ISATAP routers. Thus, Router Advertisement consistency
verification [DISC,6.2.7] is not supported by tunneling default. Routers MAY
OPTIONALLY engage in the Rtadv through IPv4. The addresses
used exchange of router advertisements with other
members of the PRL to enable this function.

5.2.4. Host Specification

Hosts periodically poll each entry in the IPv6 and PRL ("PRL(i)") by sending
unicast Router Solicitation messages using the IPv4 headers are:

ipv6_src: FE80::0:5EFE:V4ADDR_RTR
ipv6_dst: FE80::0:5EFE:V4ADDR_NODE
ipv4_src: V4ADDR_RTR
ipv4_dst: V4ADDR_NODE
- Upon receiving address
("V4ADDR_PRL(i)") and associated timer in the entry. Hosts add the Rtsol,
following variable to support the originating node performs address
autoconfiguration as described in [AUTO] polling process:

MinRouterSolicitInterval
Minimum time between sending Router Solicitations
to any router. Default and constructs:

- a fully-qualified ISATAP address for use as the source address
for an ISATAP pseudo-interface

- a default route that points suggested minimum: 15min

When PRL(i) is first added to the ISATAP router

Note (**) that list, the above procedure assumes host sets its associated
timer to MinRouterSolicitInterval.

Entries are polled when they are created (following a means for discovering
V4ADDR_RTR. We present two alternative methods short delay as
for initial solicitations [ND,6.3.7]), and when the automatic
discovery associated timer
expires.

Polling consists of V4ADDR_RTR:

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 sending Router Solicitations to the establishment of a new
well-known service name (e.g. "ISATAPGW"), administrators could pub-
lish ISATAP link-
local address constructed from the entry's IPv4 address of a gateway which implementations could use address, i.e., they
are sent to
discover V4ADDR_RTR. This method has 'FE80::0:5EFE:V4ADDR_PRL(i)' instead of 'All-Routers mul-
ticast'. They are otherwise sent in the same manner described in
[DISC,6.3.7].

When the advantage host receives a valid Router Advertisement (i.e., one that it can be
deployed immediately using existing mechanisms. However, it requires
name service lookups
satisfies the validity checks in sections 4.5 and may not always provide 5.2.2) it processes
them in the optimum
V4ADDR_RTR resolution for isolated hosts if multiple ISATAP routers
are available.

5.3. IPv4 Anycast for ISATAP routers

[6TO4ANY] proposes an IPv4 anycast prefix for 6to4 relay routers. same manner described in [DISC,6.3.4]. The proposal suggests an IPv4 prefix assignment '192.88.99.0/24'
where host addition-
ally resets the single timer associated with the PRL entry that matches the
network-layer source address '192.88.99.1' is assigned as in the "6to4 IPv6
relay anycast address". We propose analogous assignments for Router Advertisement. The timer
is reset to either 0.5 * (the minimum value in the pur-
pose of an "ISATAP router anycast address". (Whether the reservation lifetime or
valid lifetime of a second /32 assignment from the 6to4 IPv4 anycast prefix proposed
in [6TO4ANY] would be possible, any on-link prefixes advertised) or a separate prefix assignment would
be required MinRouterSoli-
citInterval; whichever is a matter of debate longer.

6. ISATAP Deployment Considerations

6.1. Host And Router Deployment Considerations

For hosts, if an underlying link supports both IPv4 (over which ISA-
TAP is implemented) and TBD.) also supports IPv6 natively, then ISATAP routers would advertise MAY
be enabled if the ISATAP native IPv6 layer does not receive Router Adver-
tisements (i.e., does not have connection with an IPv6 router). After
a non-link-local address has been configured and a default router anycast prefix via
acquired on the intra-domain IPv4 routing infrastructure. Isolated IPv6 nodes
would then use native link, the host MAY discontinue the 'Router
Polling Process' process specified in section 5.2.4 and allow exist-
ing ISATAP router anycast address configurations to expire as specified in
[DISC,5.3][AUTO,5.5.4]. In this way, ISATAP use will gradually dimin-
ish as IPv6 routers are widely deployed throughout the V4ADDR_RTR
IPv4 destination for off-link Rtsol's. This approach has site.

Routers MAY configure a native link to simultaneously support both
native IPv6, and also ISATAP (over IPv4). Routing will operate as
usual between these two domains. Note that the signifi-
cant advantages that:

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

- an optimum path to and native IPv6 interfaces will be distinct.

When an ISATAP router would be ensured
by intra-domain IPv4 routing
As described above, is configured, the IPv4 anycast method address used for locating its
ISATAP
routers provides significant functional advantages over the DNS
approach, while the DNS approach can interface SHOULD be implemented immediately pend-
ing added (either automatically or manually)
to the registration of a WKS site's name with IANA. While either method service records for the "ISATAP" Well-Known Ser-
vice name (e.g., by adding an A record in DNS), so it will work, be added
to the decision ISATAP Potential Router list of which to push for standardization is TBD
pending discussion at upcoming NGTRANS WG meetings.

6. Sending Rules and Routing all nodes on the link.

6.2. Site Administration Considerations

Since each node will be assigned one or more

The following considerations are noted for sites that deploy ISATAP:

- ISATAP prefixes which links are administratively reserved for use ONLY defined by a set of router
interfaces, and set of nodes which have those interface addresses
in their potential router lists. Thus, ISATAP nodes, no spe-
cial sending rules links are needed. defined by
administrative (not physical) boundaries.

- ISATAP hosts and routers can be deployed in an ad-hoc and independent
fashion. In particular, correspondent nodes
that share a common ISATAP prefix will always exchange messages using
their hosts can be deployed with little/no
advanced knowledge of existing ISATAP pseudo-interfaces, whereas nodes that do not share a
common routers, and ISATAP prefix will always exchange messages via standard IPv6
routing. When sending a message on an routers
can deployed with no reconfiguration requirements for hosts.

- ISATAP pseudo-interface, an
implementation SHOULD verify that nodes periodically send Router Solicitations to all entries
in the IPv6 next-hop address employs Potential Router List. Worst-case control traffic is on the ISATAP address construction rules described in section 4 in
order
to detect mis-configured addresses. No other sending rules are neces-
sary.

7. Address Selection

No special address selection rules are necessary.

8. Automatic Deprecation of (M x N), where 'M' is the number of routers in the Potential
Router List and 'N' is the total number of nodes on the ISATAP addresses are intended link.
The MinRouterSolicitInterval of 15min bounds control traffic for use only by
large numbers of nodes which do not
receive native IPv6 Rtadv's due to not sharing a common link even in worst-case scenarios.

- Strategic site administration, along with an
IPv6 router. When native IPv6 Rtadv's become available (such as when
an IPv6 robust host and router is deployed on a node's link), the node should con-
struct
implementations, can provide significant reductions in control
traffic. At a non-ISATAP aggregatable global IPv6 unicast address using
address auto-configuration [AUTO] minimum, site administrators SHOULD ensure that name
service records for a non-ISATAP IPv6 prefix
discovered through normal means [DISC]. After the node's native IPv6
address is populated "ISATAP" Well-Known Service name are well
maintained, and represent valid ISATAP routers.

7. IANA considerations

We propose that IANA adopt the interface identifier construction
specified in section 4.1 for the DNS, existing IANA IEEE OUI registration
('00-00-5E'). Additionally, we request that the node should eventually cease
sending Rtsol's to name "ISATAP" be
reserved in the ISATAP router IANA "Protocol and discontinue use of its ISA-
TAP pseudo-interface. Service Names" assigned numbers
document.

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] apply also to ISATAP.

Responsible IPv4 site security management is strongly encouraged. In this way, ISATAP
particular, border gateways SHOULD implement filtering to detect
spoofed IPv4 source addresses will gradually
(and automatically) disappear as IPv6 routers are widely deployed
within sites.

9. Multicast Considerations

Other works at a minimum; ip-protocol-41 filtering
SHOULD also be implemented.

If IPv4 source address filtering is not correctly implemented, the
validity checks in progress [6TO4MULTI] are currently investigating mul-
ticast addressing issues section 4.7 will not be effective in preventing
IPv6 source address spoofing.

If filtering for [6TO4]. The ip-protocol-41 is not correctly implemented, IPv6
source address format discussed in
this document spoofing is expected to clearly possible, but this can be compatible with those emerging
approaches.

10. IANA considerations

In order to support the EUI-64 elim-
inated if both IPv4 source address form described in this docu-
ment, we propose that IANA adopt filtering, and the EUI-64 Interface Identifier for-
mat specified validity checks
in section 4.2 for the existing 00-00-5E OUI owned by
IANA. No other actions 4.7 are required implemented.

[DISC,6.1.2] implies that nodes trust Router Advertisements they
receive from on-link routers, as indicated by a value of 255 in the IANA.

11. Security considerations
IPv6 'hop-limit' field. Since this field is not decremented when ip-
protocol-41 packets traverse multiple IPv4 hops [MECH,3.3], 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). This trust model is predicated on IPv4 source address filter-
ing, as described above.

The ISATAP address format does not support privacy extensions for
stateless address autoconfiguration [PRIVACY]. However, such privacy
extensions are intended primarily to avoid revealing one's MAC
address, and since the
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.

12. Implementation status

The author has implemented the mechanisms described in this draft
through modifications to interface identifier is derived from the FreeBSD 3.2-RELEASE [FBSD] operating
system with node's IPv4 address,
ISATAP addresses do not have the INRIA [INRIA] IPv6 distribution. As same level of November 12,
2001, a Linux implementation is now integrated in privacy concerns as
IPv6 addresses that use an interface identifier derived from the USAGI Linux
distribution [USAGI].

Additionally, Windows XP RC1 will implement elements MAC
address.

Acknowledgements
Some of the mechanism
proposed in this paper.

Acknowledgements

The original ideas presented in this draft were derived from work at
SRI con-
tractual work. The author recognizes that ideas similar to those in
this document may have already been presented by others with internal funds and wishes to
acknowledge any other such authors. The author also wishes to ack-
nowledge the government contract administrators contractual support. Government sponsors
who sponsored supported the
projects work include Monica Farah-Stapleton and Russell
Langan from which these works derived as well as his SRI colleagues
with whom he has discussed U.S. Army CECOM ASEO, and reviewed this work, including Monica
Farah-Stapleton, Dr. Allen Moshfegh from U.S.
Office of Naval Research. Within SRI, Dr. Mike Frankel, J. Peter Marcotullio, Mar-
cotullio, Lou Rodri-
guez, 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 Dr. provide input: Jim Bound,
Rich Draves, Cyndi Jung, Ambatipudi Sastry. Sastry, Aaron Schrader, Ole
Troan, Vlad Yasevich.

The author acknowledges valuable input from numerous authors acknowledge members of the NGTRANS community which has helped guide the direction of the draft.
The list of contributors is too long to enumerate, but the input from
the community has been vital who have
made significant contributions to the draft's evolution. Alain Durand
deserves special mention for contributing the title of this draft and
the ISATAP acronym. Additionally, Tim Gleenson and effort, including Rich Draves,
Alain Durand, Nathan Lutchansky
numerous helpful suggestions for improvement.

The author finally wishes to provide special acknowledgement to Dave
Thaler, Lutchansky, Art Shelest, Richard Draves, Margaret Wasserman, and others at Microsoft Research
for their ideas on automatic discovery of off-link IPv6 routers. Much
of
Brian Zill.

Finally, the text authors recognize that ideas similar to those in section on deployment considerations derives directly
from discussions with Dave, Art, Rich this
document may have already been presented by others and others. wish to ack-
nowledge any other such contributions.

Normative References

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

[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
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., 1997.

[ICMPv6] Conta, A. and J. Postel, "Assigned Numbers", STD 2,
USC/Information Sciences Institute, October 1994. S. Deering, "Internet Control Message
Protocol (ICMPv6) for the Internet Protocol Version 6
(IPv6) Specification", RFC 2463, December 1998.

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

[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",
RFC 3068, June 2001.

[6TO4MULTI] Thaler, D., "Support for Multicast over 6to4 Networks",
draft-ietf-ngtrans-6to4-multicast-00.txt (work in pro-
gress) 2460.

[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-
ietf-
ipngwg-default-addr-select-06.txt (work in progress)

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

[USAGI] http://www.linux-ipv6.org

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

[6BONE] Rockell, R.,

[NAT] Egevang, K., and R. Fink, P. Francis, "The IP Network Address
Translator (NAT)", RFC 2772, February 2000. 1631, May 1994.

[PRIVATE] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.
J., G.,
and E. Lear, "Address Allocation for Private Internets",
RFC 1918, 1918, February 1996.

Informative References

[6OVER4] 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 1996. 2001.

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

[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
Phone: (650)-859-3144
Email: templin@erg.sri.com

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

Mohit Talwar
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052-6399
Phone: +1 425 705 3131
EMail: mohitt@microsoft.com

Dave Thaler
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052-6399
Phone: +1 425 703 8835
EMail: dthaler@microsoft.com

APPENDIX A: Major Changes

changes from version 02 to version 03:

- Added contributing co-authors

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

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

- Added applicability statement

changes from version 01 to version 02:

- Cleaned up text and tightened up terminology. Changed "IPv6 destination
address" to "IPv6 next-hop address" under "sending rules". Changed
definition of ISATAP prefix to include link and site-local. Changed
language in sections 4 and 5

changes from version 00 to version 01:

- Revised draft to require different /64 prefixs 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.

changes from personal draft to version 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.

Intellectual Property

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