INTERNET-DRAFT                              R. Hinden, Ipsilon Networks
June 12,
July 16, 1997                                          M. O'Dell, UUNET
                                                      S. Deering, Cisco

           An IPv6 Aggregatable Global Unicast Address Format



Status of this Memo

   This document is an Internet Draft.  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.

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   Please check the 1id-abstracts.txt listing contained in the internet-
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   This internet draft expires on December 13, 1997. January 17, 1998.

1.0 Introduction

   This document defines an IPv6 aggregatable global unicast address
   format for use in the Internet.  The address format defined in this
   document is consistent with the IPv6 Protocol [IPV6] and the "IPv6
   Addressing Architecture" [ARCH].  It is designed to facilitate
   scalable Internet routing.

   This documented replaces RFC 2073, "An IPv6 Provider-Based Unicast
   Address Format".  RFC 2073 will become historic.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC 2119].

2.0 Overview of the IPv6 Address

   IPv6 addresses are 128-bit identifiers for interfaces and sets of
   interfaces.  There are three types of addresses: Unicast, Anycast,
   and Multicast.  This document defines a specific type of Unicast

   In this document, fields in addresses are given specific names, for
   example "subnet".  When this name is used with the term "ID" (for
   "identifier") after the name (e.g., "subnet ID"), it refers to the
   contents of the named field.  When it is used with the term "prefix"
   (e.g.  "subnet prefix") it refers to all of the addressing bits to
   the left of and including this field.

   IPv6 unicast addresses are designed assuming that the internet Internet
   routing system makes forwarding decisions based on a "longest prefix
   match" algorithm on arbitrary bit boundaries and does not have any
   knowledge of the internal structure of IPv6 addresses.  The structure
   in IPv6 addresses is for assignment and allocation.  The only
   exception to this is the distinction made between unicast and
   multicast addresses.

   The specific type of an IPv6 address is indicated by the leading bits
   in the address.  The variable-length field comprising these leading
   bits is called the Format Prefix (FP).

   This document defines an address format for the 001 (binary) Format
   Prefix for Aggregatable Global Unicast addresses. The same address
   format could be used for other Format Prefixes, as long as these
   Format Prefixes also identify IPv6 unicast addresses.  Only the "001"
   Format Prefix is defined here.

3.0 IPv6 Aggregatable Global Unicast Address Format

   This document defines an address format for the IPv6 aggregatable
   global unicast address assignment.  The authors believe that this
   address format will be widely used for IPv6 nodes connected to the
   Internet.  This address format is designed to support both the
   current provider-based aggregation and a new type of exchange-based
   aggregation.  The combination will allow efficient routing
   aggregation for both sites that connect directly to providers and for
   sites that connect to exchanges.  Sites will have the choice to
   connect to either type of aggregation entity.

   While this address format is designed to support exchange-based
   aggregation (in addition to current provider-based aggregation) it is
   not dependent on exchanges for it's overall route aggregation
   properties.  It will provide efficient route aggregation with only
   provider-based aggregation.

   Aggregatable addresses are organized into a three level hierarchy:

      - Public Topology
      - Site Topology
      - Interface Identifier

   Public topology is the collection of providers and exchanges who
   provide public Internet transit services.  Site topology is local to
   a specific site or organization which does not provide public transit
   service to nodes outside of the site.  Interface identifiers identify
   interfaces on links.

        ______________                  ______________
    --+/              \+--------------+/              \+----------
      (       P1       )    +----+    (       P3       )  +----+
      +\______________/     |    |----+\______________/+--|    |--
      |                  +--| X1 |                       +| X2 |
      | ______________  /   |    |-+    ______________  / |    |--
      +/              \+    +-+--+  \  /              \+  +----+
      (       P2       )     / \     +(      P4        )
    --+\______________/     /   \      \______________/
           |               /     \           |      |
           |              /       |          |      |
           |             /        |          |      |
          _|_          _/_       _|_        _|_    _|_
         /   \        /   \     /   \      /   \  /   \
        ( S.A )      ( S.B )   ( P5  )    ( P6  )( S.D S.C )
         \___/        \___/     \___/      \___/  \___/
                                  |          / \
                                 _|_       _/_  \   ___
                                /   \     /   \  +-/   \
                               ( S.E S.D )   ( S.F S.E )  ( S.G S.F )
                                \___/     \___/    \___/

   As shown in the figure above, the aggregatable address format is
   designed to support long-haul providers (shown as P1, P2, P3, and
   P4), exchanges [EXCH] (shown as X1 and X2), multiple levels of
   providers (shown at P5 and P6), and subscribers (shown as S.x)
   Exchanges (unlike current NAPs, FIXes, etc.) will allocate IPv6
   addresses.  Organizations who connect to these exchanges will also
   subscribe (directly, indirectly via the exchange, etc.) for long-
   haul long-haul
   service from one or more long-haul providers.  Doing so, they will
   achieve addressing independence from long-haul transit providers.
   They will be able to change long-haul providers without having to
   renumber their organization.  They can also be multihomed via the
   exchange to more than one long-haul provider without having to have
   address prefixes from each long-haul provider.  Note that the
   mechanisms used for this type of provider selection and portability
   are not discussed in the document.

3.1 Aggregatable Global Unicast Address Structure

   The aggregatable global unicast address format is as follows:

      | 3 |  13 |    32     |   16   |          64 bits               |
      |FP | TLA |   NLA* NLA ID    |  SLA* SLA ID |         Interface ID           |
      |   | ID  |           |        |                                |

      <--Public Topology--->   Site
                                      <------Interface Identifier----->


      FP           Format Prefix (001)
      TLA ID       Top-Level Aggregator
      NLA* Aggregation Identifier
      NLA ID       Next-Level Aggregator(s)
      SLA* Aggregation Identifier
      SLA ID       Site-Level Aggregator(s) Aggregation Identifier
      INTERFACE ID Interface Identifier

   The following sections specify each part of the IPv6 Aggregatable
   Global Unicast address format.

3.2 Top-Level Aggregator Aggregation ID

   Top-Level Aggregators (TLA) Aggregation Identifiers (TLA ID) are the top level in the
   routing hierarchy.  Default-free routers must have a routing table
   entry for every active TLA. TLA ID and will probably have additional
   entries providing routing information for the TLA ID in which they
   are located.  They may have additional entries, entries in order to optimize
   routing for their specific topology, but the routing topology at all
   levels must be designed to minimize the number of additional entries
   fed into the default free routing tables.

   This addressing format supports 8,192 (2^^13) TLA's. (2^13) TLA ID's.  Additional
   TLA ID's may be added by using this format for additional format
   prefixes.  The addition of another FP will add another 8,192 TLA's.

3.2.1 Assignment of TLAs

   TLAs are assigned to organizations providing public transit topology.
   They are specifically not assigned to organizations only providing
   leaf or private transit topology. TLA assignment does not imply
   ownership.  It does imply stewardship over valuable Internet

   The IAB and IESG have authorized the Internet Assigned Numbers
   Authority (IANA) as the appropriate entity to have the responsibility
   for the management of the IPv6 address space as defined in [ALLOC].

   The IANA will assign small blocks of TLAs to IPv6 registries.  The
   registries will assign the TLAs to organizations meeting the
   requirements for TLAs.  When the registries have assigned all of
   their TLAs they can request that the IANA give them another block.
   The blocks do not have to be contiguous.  The IANA may also assign
   TLAs to organizations directly.

   Organizations assigned TLAs are required to meet the following

    - Must have a plan to offer public native IPv6 service within 6
      months from assignment.  Plan must include plan for NLA

    - Plan or track record providing public internet transit service on
      fair, reasonable, and non-discriminatory terms, to other
      providers.  TLAs must not be assigned to organizations that are
      only providing leaf service even if multihomed.

    - Must provide registry services on fair, reasonable, and non-
      discriminatory terms, for the NLA address space it is responsible
      for under its TLA.  This must include both sites and next level

    - Must provide transit routing and forwarding to all assigned TLAs
      on fair, reasonable, and non-discriminatory terms.  Organizations
      are not allowed to filter out any specific TLA's (except
      temporarily rules for diagnostic purposes or emergency repair purposed).

    - Periodically (interval set by registry) provide to registry
      utilization statistics of the TLA it has custody of.  The
      organization must also show evidence of carrying TLA routing and
      transit traffic.  This can be in the form of traffic statistics,
      traceroutes, routing table dumps, or similar means.

   Organizations which ID assignment are given custody of a TLA and fail to continue
   to meet these may have the TLA custody revoked. defined in [TLAASN].

3.3 Next-Level Aggregator(s) Aggregation Identifier

   Next-Level Aggregator(s) Aggregation Identifier's are used by TLA's organizations
   assigned a TLA ID to create an addressing hierarchy and to identify
   sites.  The TLA organization can assign the top part of the NLA ID in a
   manner to create an addressing hierarchy appropriate to its network.
   It can use the remainder of the bits in the field to identify sites
   it wishes to serve.  This is shown as follows:

         |  n  |      32-n bits     |   16   |    64 bits      |
         |NLA1 |      Site ID       |  SLA* SLA ID | Interface ID    |

   Each organization assigned a TLA ID receives 32 bits of NLA* NLA ID space.
   This NLA* NLA ID space allows each
   TLA organization to provide service to about
   approximately as many organizations as the current IPv4 internet Internet can
   support total nodes.

   The TLAs

   Organizations assigned TLA ID's may also support NLAs NLA ID's in their
   own Site ID space.  This allows the TLAs organization assigned a TLA ID to
   provide service to organizations providing public transit service and
   to organizations who do not.  The organizations
   providing not provide public transit service become NLA's themselves. service.  These NLAs
   organizations receiving an NLA ID may also choose to use their Site
   ID space to support other NLAs. NLA ID's.  This is shown as follows:

         |  n  |      32-n bits     |   16   |    64 bits      |
         |NLA1 |      Site ID       |  SLA* SLA ID | Interface ID    |

               |  m  |    32-n-m    |   16   |    64 bits      |
               |NLA2 |   Site ID    |  SLA* SLA ID | Interface ID    |

                     |  o  |32-n-m-o|   16   |    64 bits      |
                     |NLA3 | Site  |  SLA* ID| SLA ID | Interface ID    |

   The NLA delegation works in the same manner as CIDR delegation in
   IPv4 [CIDR].  TLAs are required to assume registry duties rules for the
   NLAs.  Each level of NLA is required to assume registry duties for
   the next level NLA. ID assignment are defined in [TLAASN].

   The design of the bit layout of the NLA ID space for a specific TLA
   ID is left to the organization responsible for that TLA. TLA ID.  Likewise
   the design of the bit layout of the next level NLA ID is the
   responsibility of the previous level NLA. NLA ID.  It is recommended that
   organizations assigning NLA address space use "slow start" allocation
   procedures as is currently done with IPV4 IPv4 CIDR blocks.

   The design of an NLA ID allocation plan is a tradeoff between routing
   aggregation efficiency and flexibility.  Creating hierarchies allows
   for greater amount of aggregation and results in smaller routing
   tables.  Flat NLA ID assignment provides for easier allocation and
   attachment flexibility flexibility, but results in larger routing tables.

3.4 Site-Level Aggregator(s) Aggregation Identifier

   The SLA* SLA ID field is used by an individual organization to create its
   own local addressing hierarchy and to identify subnets.  This is
   analogous to subnets in IPv4 except that each organization has a much
   greater number of subnets.  The 16 bit SLA* SLA ID field support 65,535
   individual subnets.

   Organizations may choose to either route their SLA* SLA ID "flat" (e.g.,
   not create any logical relationship between the SLA identifiers which that
   results in larger routing tables), or to create a two or more level
   hierarchy (which (that results in smaller routing tables) in the SLA* SLA ID
   field.  The latter is shown as follows:

         |  n  |   16-n     |              64 bits                |
         |SLA1 |   Subnet   |            Interface ID             |

               | m  |16-n-m |              64 bits                |
               |SLA2|Subnet |            Interface ID             |

   The approach chosen for how to the structure of structuring an SLA* SLA ID field is the
   responsibility of the individual organization.

   The number of subnets supported in this address format should be
   sufficient for all but the largest of organizations.  Organizations
   which need additional subnets can arrange with the organization they
   are obtaining internet Internet service from to obtain additional site
   identifiers and use this to create additional subnets.

3.5 Interface ID

   Interface identifiers are used to identify interfaces on a link.
   They are required to be unique on that link.  They may also be unique
   over a broader scope.  In many cases an interface's identifier will
   be the same as that or be based on the interface's link-layer address.
   Interface IDs used in the aggregatable global unicast address format
   are required to be 64 bits long and to be constructed in IEEE EUI-64
   format [EUI-64].  These identifiers may have global scope when a
   global token (e.g., IEEE 48bit MAC) is available or may have local
   scope where a global token is not available (e.g., serial links,
   tunnel end-points, etc.).  The "u" bit (universal/local bit in IEEE
   EUI-64 terminology) in the EUI-64 identifier must be set correctly,
   as defined in [ARCH], to indicate global or local scope.

   The procedures for creating EUI-64 based Interface Identifiers is
   defined in [ARCH].  The details on forming interface identifiers is
   defined in the appropriate "IPv6 over <link>" specification such as
   "IPv6 over Ethernet" [ETHER], "IPv6 over FDDI" [FDDI], etc.

4.0 Acknowledgments

   The authors would like to express our thanks to Thomas Narten, Bob
   Fink, Matt Crawford, Allison Mankin, Jim Bound, Christian Huitema,
   Scott Bradner, Brian Carpenter, and John Stewart. Stewart for their review and
   constructive comments.

5.0 References

   [ALLOC]   IAB and IESG, "IPv6 Address Allocation Management",
             RFC1881, December 1995.

   [ARCH]    Hinden, R., "IP Version 6 Addressing Architecture",
             Internet Draft, <draft-ietf-ipngwg-addr-arch-00.txt>, May <draft-ietf-ipngwg-addr-arch-v2-02.txt>,
             July 1997.

   [AUTH]    Atkinson, R., "IP Authentication Header", RFC1826, August

   [AUTO]    Thompson, S., Narten T., "IPv6 Stateless Address
             Autoconfiguration", RFC1971, August 1996.

   [CIDR]    Fuller, V., T. Li, K. Varadhan, J. Yu, "Supernetting: an
             Address Assignment and Aggregation Strategy", RFC1338.

   [ETHER]   Crawford, M., "Transmission of IPv6 Packets over Ethernet
             Networks", Internet Draft, <draft-ietf-ipngwg-trans-
             ethernet-00.txt>, March 1997.

   [EUI64]   IEEE, "Guidelines for 64-bit Global Identifier (EUI-64)
             Registration Authority",
             March 1997.

   [EXCH]    Hinden, R.,    Huitema, C. C., R. Hinden, "Internet Exchanges", document
             under preparation.

   [FDDI]    Crawford, M., "Transmission of IPv6 Packets over FDDI
             Networks", Internet Draft, <draft-ietf-ipngwg-trans-fddi-
             net-00.txt>, March 1997.

   [IPV6]    Deering, S., Hinden, R., Editors, "Internet Protocol,
             Version 6 (IPv6) Specification", RFC1883, December 1995.

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", RFC2119, BCP14, March 1997.

   [TLAASN]  Hinden, R., "TLA and NLA Assignment Rules", Internet Draft,
             <draft-ietf-ipngwg-tla-assignment-00.txt>, July 1997.

6.0 Security Considerations

   Documents of this type

   IPv6 addressing documents do not directly have any direct impact the security of the on Internet
   infrastructure or its applications. security.  Authentication of IPv6 packets is defined
   in [AUTH].

7.0 Authors' Addresses

   Robert M. Hinden                     phone: 1 408 990-2004
   Ipsilon Networks, Inc.               email:
   232 Java Drive
   Sunnyvale, CA 94089

   Mike O'Dell                          phone: 1 703 206-5890
   UUNET Technologies, Inc.             email:
   3060 Williams Drive
   Fairfax, VA 22030

   Stephen E. Deering                   phone: 1 408 527-8213
   Cisco Systems, Inc.                  email:
   170 West Tasman Drive
   San Jose, CA 95134-1706