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)




   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

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-

   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
   The list of Internet-Draft Shadow Directories can be accessed at

   Copyright Notice

   Copyright (C) The Internet Society (2001).  All Rights Reserved.

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.

   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
     - 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

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:

     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 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|
    |  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:

    |  OUI ("00-00-5E"+u+g)           64 bits            |  TYPE     32 bits   |  TSE    32 bits     |          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)

   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:


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


   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-

    | 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
   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:


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


   Similarly, we can construct the link-local link |

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


   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:


   has a node with both prefix of '3FFE:1a05:510:1111::/64' and an ISATAP link format inter-
   face identifier with embedded IPv4 address: ''.  The
   address is alternately written as:


   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:


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

   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:


   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-

   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:


     - 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

   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:

                   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

   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

   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 ''
   where host addition-
   ally resets the single timer associated with the PRL entry that matches the
   network-layer source address '' 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
       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
   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
   to detect mis-configured addresses. No other sending rules are neces-

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-
       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

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

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

   Some of the mechanism
   proposed in this paper.


   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
   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-
              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",
              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-
              ipngwg-default-addr-select-06.txt (work in progress)




   [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

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

      Mohit Talwar
      Microsoft Corporation
      One Microsoft Way
      Redmond, WA  98052-6399
      Phone: +1 425 705 3131

      Dave Thaler
      Microsoft Corporation
      One Microsoft Way
      Redmond, WA  98052-6399
      Phone: +1 425 703 8835

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.

     - 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:

     - 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.

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