RFC 2921 (rfc2921) - Page 2 of 7

6BONE pTLA and pNLA Formats (pTLA)

RFC 2921              6BONE pTLA and pNLA Formats         September 2000


   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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