CS Knowledge Base

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




           An IPv6 Aggregatable Global Unicast Address Format


                <draft-ietf-ipngwg-unicast-aggr-00.txt>



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.

   Internet Drafts are draft documents valid for a maximum of six
   months.  Internet Drafts may be updated, replaced, or obsoleted by
   other documents at any time.  It is not appropriate to use Internet
   Drafts as reference material or to cite them other than as a
   ``working draft'' or ``work in progress.''

   Please check the 1id-abstracts.txt listing contained in the internet-
   drafts Shadow Directories on nic.ddn.mil, nnsc.nsf.net,
   nic.nordu.net, ftp.nisc.sri.com, or munnari.oz.au to learn the
   current status of any Internet Draft.

   This internet draft expires on November 17, 1997.


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",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this



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   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
   address.

   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.

   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 aggregation
   called exchanges.  The combination will allow efficient routing
   aggregation for both sites that connect directly to providers and
   sites that connect to exchanges.  Sites will have the choice to
   connect to either type of aggregation entity.

   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



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   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.E )   ( S.F )  ( S.G )
                                \___/     \___/    \___/


   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 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.

   IPv6 unicast addresses are designed assuming that the 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.



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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*    |  SLA*  |         Interface ID           |
      +---+-----+-----------+--------+--------------------------------+


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

   Where

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

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


3.2 Top-Level Aggregator

   Top-Level Aggregators (TLA) are the top level in the routing
   hierarchy.  Default-free routers will, at a minimum, have a routing
   table entry for every active TLA.

   This addressing format supports 8,192 (2^^13) TLA's.  Additional TLA
   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
   property.

   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].



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   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 to give them another block.
   The blocks do not have to be contiguous.  The IANA may also assign
   TLAs to organizations directly.

   TLA assignment requirements are as follows:

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

    - Plan or track record providing public internet transit service to
      other providers.  TLAs should not be assigned to organization that
      are only providing leaf service even if multihomed.

    - Must provide registry services for the NLA address space it is
      responsible for under its TLA.  This must include both sites and
      next level providers.

    - Must provide transit routing and forwarding to all assigned TLAs.
      Organization is not allowed to filter out any specific TLA's
      (except temporarily for diagnostic purposes).

    - Periodically (interval set by registry) provide to registry
      utilization statistics of the TLA it has custody of.  The
      organization must also provide traffic statistics on amounts of
      traffic for transit TLA traffic.

   Organizations which are given custody of a TLA and fail to continue
   to meet these (or other future requirements defined by the IANA) may
   have the TLA custody revoked.


3.3 Next-Level Aggregator(s)

   Next-Level Aggregator(s) are used by TLA's to create an addressing
   hierarchy and to identify sites.  The TLA can assign the top part of
   the NLA 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         |  SLA*  | Interface ID    |
         +-----+--------------------+--------+-----------------+




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

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

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

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

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

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

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


3.4 Site-Level Aggregator(s)

   The SLA* 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* field support 65,535
   individual subnets.

   Organizations may choose to either route their SLA* "flat" (e.g., not



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   create any logical relationship between the SLA identifiers), or to
   create a two or more level hierarchy in the SLA* 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 an SLA* field is the
   responsibility of the individual organization.

   The number of subnets supported should be sufficient for all but the
   largest of organizations.  Organizations which need additional
   subnets can arrange with the organization they are obtaining 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 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].  Interface identifiers formed using EUI-64
   identifiers may have global scope when a global token is available or
   may have local scope where a global token is not available (e.g.,
   serial links, tunnel end-points, etc.).  Where EUI-64 identifiers are
   used it is required that the "u" bit (universal/local bit in IEEE
   EUI-64 terminology) be set correctly.

   The construction of Interface Identifiers constructed in EUI-64
   format 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.






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4.0 Acknowledgments

   The authors would like to express our thanks to Thomas Narten, Bob
   Fink, Matt Crawford, Allison Mankin, Jim Bound, Christian Huitema,
   and Scott Bradner 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
             1997.

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

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

     [ETHER] M. Crawford, "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",
             http://standards.ieee.org/db/oui/tutorials/EUI64.html,
             March 1997.

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

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

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

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








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6.0 Security Considerations

   Documents of this type do not directly impact the security of the
   Internet infrastructure or its applications.


7.0 Authors' Addresses

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

   Mike O'Dell                          phone: 1 703 206-5890
   UUNET Technologies, Inc.             email: mo@uunet.uu.net
   3060 Williams Drive
   Fairfax, VA 22030
   USA

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


























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