6BONE pTLA and pNLA Formats (pTLA)
draft-ietf-ngtrans-6bone-ptla-00

INTERNET-DRAFT                                          Bob Fink, ESnet
March 10, 2000

                   6BONE pTLA and pNLA Formats (pTLA)

                  <draft-ietf-ngtrans-6bone-ptla-00.txt>

Abstract

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's) and pseudo Next-Level Aggregation Identifiers (pNLA's).

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
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is inappropriate to use Internet-Drafts as reference material or to cite
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The list of current Internet-Drafts can be accessed at
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This Internet Draft expires September 10, 2000.

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.

Contents

Status of this Memo..........................................

1.  Introduction.............................................

2.  6BONE pTLA/pNLA Format...................................

3.  Security Considerations..................................

4.  Change Log...............................................

REFERENCES...................................................

AUTHOR'S ADDRESS.............................................

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).

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 preffix 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 aggegation (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.

          |     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 if became clear that the 6bone would become a useful testbed for
transition, in addition to its early role asa 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,

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.

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.

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 infra-
structure security.

4.  Change Log

Changes since version -00 of the draft:

none yet, still on -00

REFERENCES

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

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

[HARDEN] R. Rockell, R. Fink, "6Bone Backbone Routing Guidelines",
RFC xxxx, December 1999. Replaces RFC 2546.

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

[6BONE-TLA] R. Hinden, R. Fink, 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

-end