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 RFC2471, "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 RFC2471 [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 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.
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,
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
infrastructure security.
References
[ADDRARCH] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC2373, July 1998.
[AGGR] Hinden, R., O"Dell, M. and S. Deering, "An IPv6
Aggregatable Global Unicast Address Format", RFC2374,
July 1998.
[HARDEN] Rockell, R. and R. Fink, "6Bone Backbone Routing
Guidelines", RFC2772, February 2000.
[KEYWordS] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC2119, March 1997.
[6BONE-TLA] Hinden, R., Fink, R. and J. Postel, "IPv6 Testing Address
Allocation", RFC2471, 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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