path: root/doc/rfc/rfc2921.txt

Network Working Group                                            B. Fink
Request for Comments: 2921                                         ESnet
Category: Informational                                   September 2000


                   6BONE pTLA and pNLA Formats (pTLA)

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2000).  All Rights Reserved.

Abstract

   This memo defines how the 6bone uses the 3FFE::/16 IPv6 address
   prefix, allocated in RFC 2471, "IPv6 Testing Address Allocation",
   [6BONE-TLA], to create pseudo Top-Level Aggregation Identifiers
   (pTLA's) and pseudo Next-Level Aggregation Identifiers (pNLA's).

Acknowledgements

   The address formats here are contributions of various early
   participants of the 6bone testbed project, and of the IPng and
   NGtrans IETF working groups.

Table of Contents

   1.  Introduction................................................. 1
   2.  6BONE pTLA/pNLA Format....................................... 2
   3.  Security Considerations...................................... 6
   References....................................................... 6
   Author's Address................................................. 6
   Full Copyright Statement......................................... 7

1. Introduction

   This memo defines how the 6bone uses the 3FFE::/16 IPv6 address
   prefix, allocated in RFC 2471 [6BONE-TLA], to create pseudo Top-Level
   Aggregation Identifiers (pTLA) and pseudo Next-Level Aggregation
   Identifiers (pNLA).






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   The guiding specifications for IPv6 addressing relating to the 6bone
   prefix, and the pTLA and pNLA formats, are "IP Version 6 Addressing
   Architecture"  [ADDRARCH], and "An IPv6 Aggregatable Global Unicast
   Address Format" [AGGR].

   The purpose of creating pseudo TLA and NLA formats for the 6bone is
   to provide a prototype of the actual TLA and NLA formats as they
   might be used in production IPv6 networks. To do this economically,
   using only a minimum of real production IPv6 address space, a single
   TLA, 3FFE::/16, was reserved by the IANA (Internet Assigned Numbers
   Authority) for testing on the 6bone. Thus it was necessary to define
   a pretend-to-be, or pseudo, TLA and NLA structure to use under the
   3FFE::/16 prefix.

   Given the 48-bit length of the IPv6 Aggregatable Global Unicast
   Address external routing prefix (that contains the TLA and NLA
   identifiers), there is enough room to extend the TLA ID to contain a
   pTLA and shorten the NLA ID to become a pNLA. This document specifies
   this.

   In early 1999, it was decided to change the 6bone's pTLA format to
   allow greater expansion of the testbed network, thus accommodating
   more than the original 256 pTLA-s. Thus there are now two 6bone pTLA
   and pNLA formats. This document specifies this.

2. 6BONE pTLA and pNLA Formats

2.1 Original 8-bit pTLA and 24-bit pNLA Format

   The original pTLA and pNLA format was intended to accommodate 256
   pTLA-s, i.e., backbone networks carrying IPv6 transit traffic.

   The original TLA and NLA ID-s as specified in [AGGR] are as follows:

      | 3 |  13 |          32         |   16   |    64 bits      |
      +---+-----+---------------------+--------+-----------------+
      |001| TLA |       NLA ID        | SLA ID | Interface ID    |
      +---+-----+---------------------+--------+-----------------+

   The TLA value 1FFE was assigned to the 6bone, which when viewed with
   the 3-bit format prefix in prefix notation form is 3FFE::/16.

   The first 8-bits of the NLA ID space are assigned as the pTLA that
   defines the top level of aggregation (backbone) for the 6bone. This
   provides for 256 6bone backbone networks, or pTLA-s, and leaves a
   24-bit pNLA ID for each pTLA to assign as needed.





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      |     16    |  8  |     24      |   16   |    64 bits      |
      +-+---------+-----+-------------+--------+-----------------+
      |  0x3FFE   |pTLA |     pNLA    | SLA ID | Interface ID    |
      +-+---------+-----+-------------+--------+-----------------+

   In prefix notation form the pTLA is 3FFE:nn00::/24, where nn is the
   pTLA assignment.

   The remaining NLA ID space can be used by each pTLA for their
   downward aggregated delegation:

      |  n  |      24-n bits     |   16   |    64 bits      |
      +-----+--------------------+--------+-----------------+
      |pNLA1|       Site         | SLA ID | Interface ID    |
      +-----+--------------------+--------+-----------------+

            |  m  |    24-n-m    |   16   |    64 bits      |
            +-----+--------------+--------+-----------------+
            |pNLA2|    Site      | SLA ID | Interface ID    |
            +-----+--------------+--------+-----------------+

                  |  o  |24-n-m-o|   16   |    64 bits      |
                  +-----+--------+--------+-----------------+
                  |pNLA3|  Site  | SLA ID | Interface ID    |
                  +-----+--------+--------+-----------------+

   The pNLA delegation works in the same manner as specified in [AGGR].
   pTLA's are required to assume registry duties for the pNLA's below
   them, pNLA1's for those below them, etc.

2.2 New 12-bit pTLA and 20-bit pNLA Format

   After it became clear that the 6bone would become a useful testbed
   for transition, in addition to its early role as a testbed for
   specifications and implementations, the 6bone community decided to
   expand the size of the pTLA ID.

   Several important decisions regarding this expansion of the pTLA
   field are:

   1. to leave the currently allocated 8-bit pTLA-s in use until the
      space was needed, thus relying on a range value check to indicate
      the new pTLA format,

   2. to use a modulo 4-bit sized pTLA ID to make reverse path entry
      into the DNS easier,





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   3. given 2. above, to keep the pTLA ID size as small as possible
      to not restrict pNLA ID size.

   Therefore, the first 12-bits of the NLA ID space are assigned as the
   pTLA that defines the top level of aggegation (backbone) for the
   6bone. This would eventually provide for 4096 6bone backbone
   networks, or pTLA-s, and leaves a 20-bit pNLA ID for each pTLA to
   assign as needed.

      |     16    |   12  |   20      |   16   |    64 bits      |
      +-+---------+-------+-----------+--------+-----------------+
      |  0x3FFE   | pTLA  |   pNLA    | SLA ID | Interface ID    |
      +-+---------+-------+-----------+--------+-----------------+

   In prefix notation form the pTLA is 3FFE:nnn0::/28, where nnn is the
   pTLA assignment. However, as the existing 8-bit pTLA's are being left
   in use for the present, the nnn value starts at 0x800 for now, thus
   yielding only 2048 pTLA's in this new format.

   The remaining NLA ID space can be used by each pTLA for their
   downward aggregated delegation:

      |  n  |      20-n bits     |   16   |    64 bits      |
      +-----+--------------------+--------+-----------------+
      |pNLA1|       Site         | SLA ID | Interface ID    |
      +-----+--------------------+--------+-----------------+

            |  m  |    20-n-m    |   16   |    64 bits      |
            +-----+--------------+--------+-----------------+
            |pNLA2|    Site      | SLA ID | Interface ID    |
            +-----+--------------+--------+-----------------+

                  |  o  |20-n-m-o|   16   |    64 bits      |
                  +-----+--------+--------+-----------------+
                  |pNLA3|  Site  | SLA ID | Interface ID    |
                  +-----+--------+--------+-----------------+

   As with the original pTLA format, the pNLA delegation works in the
   same manner as specified in [AGGR]. pTLA's are required to assume
   registry duties for the pNLA's below them, pNLA1's for those below
   them, etc.

2.3 Example Format For pNLA's

   An example usage of the pNLA space is given to demonstrate what is
   reasonable and possible. It should not be assumed that this implies
   the pNLA space must be used this way. As the new pTLA and pNLA format
   is now the default, the example here assumes the 20-bit pNLA format.



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   The following example provides for up to 255 intermediate transit
   ISP's (called pNLA1 below). The pNLA1 value of zero is meant to
   indicate that there is no intermediate transit ISP between the
   backbone pTLA network and the end user site.

      |<-----20-bit pNLA ID----->|
      |                          |
      |  8  |       12 bits      |   16   |    64 bits      |
      +-----+--------------------+--------+-----------------+
      |pNLA1|      Site  ID      | SLA ID | Interface ID    |
      +-----+--------------------+--------+-----------------+

   Intermediate transit networks (pNLA1's) would assign uniques Site
   ID's for eachend user site served.

   As an example of this, assuming a backbone pTLA of 0x800, no
   intermediate transit ISP (thus a pNLA1 of 0x00) and a sequential site
   ID (with start at the right edge numbering) of 0x0001, the routing
   prefix for the first site would look like:

            3FFE:8000:0001/48
     6bone _|||| |||| ||||___site
                 |||| |
     b/b site____|||| |
                    | |
     transit________|_|

   Another example of this usage, assuming the same backbone pTLA1 of
   0x800 and an intermediate transit ISP under it (numbering from the
   left edge) with an NLA1 of 0x80, and a sequential site ID of 0x0001,
   the routing prefix for the first site connected would look like:

            3FFE:0180:0001/48
     6bone _|||| |||| ||||___site
                 ||||
     b/b site____||||
                   ||
     transit_______||

   Note 1: the two sites numbered 0x001 in the above examples are really
   two different sites as their pNLA1 authority above them is different
   (i.e., in the first case no transit exists thus the site is directly
   connected to the pTLA backbone ISP, and in the second case the site
   is directly connected to intermediate transit ISP 0x80).

   Note 2: there would be nothing to prevent an pNLA1 transit site from
   further allocating pNLA's below, but that becomes the policy of the
   pTLA and pNLA's above them to work out.



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   Note 3: The 6bone registry, which is a RIPE-style database for
   documenting IPv6 sites connected to the 6bone, has an "inet6num"
   object to allow documentation of all IPv6 addresses allocated.

3.  Security Considerations

   IPv6 addressing documents do not have any direct impact on Internet
   infrastructure security.

References

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

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

   [HARDEN]    Rockell, R. and R. Fink, "6Bone Backbone Routing
               Guidelines", RFC 2772, February 2000.

   [KEYWORDS]  Bradner, S., "Key words for use in RFCs to Indicate
               Requirement Levels", BCP 14, RFC 2119, March 1997.

   [6BONE-TLA] Hinden, R., Fink, R. and J. Postel, "IPv6 Testing Address
               Allocation", RFC 2471, December 1998.

Author's Address

   Bob Fink, ESnet
   Lawrence Berkeley National Lab
   MS 50A-3111
   1 Cyclotron Road
   Berkeley, CA 94720
   USA

   Phone: +1 510 486 5692
   Fax:   +1 510 486 4790
   EMail: fink@es.net












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Full Copyright Statement

   Copyright (C) The Internet Society (2000).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
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   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
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   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
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   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
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Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.



















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