Revised NSAPA mapping

Brian Carpenter CERN-CN <brian@dxcoms.cern.ch> Mon, 18 July 1994 12:12 UTC

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From: Brian Carpenter CERN-CN <brian@dxcoms.cern.ch>
Message-Id: <9407181210.AA25994@dxcoms.cern.ch>
Subject: Revised NSAPA mapping
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Date: Mon, 18 Jul 1994 14:10:51 +0200
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[Acknowledgements for useful comments: Scott Bradner, John Curran,
Bob Hinden, Yakov Rekhter. And for the main improvement: Cyndi Jung.]

BTW, I haven't bothered to write down a mapping for NSAPAs inside
the BigTen 24-byte address format, but it is clearly trivial.

  Brian

1. NSAPAs inside a 16-byte IPng address


 The main goal of this embedding is to allow pre-existing  NSAPA
 allocations, profiled for CLNP, to be re-used for IPng routing. It does
 not offer a mapping for arbitrary NSAPAs.

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 0-3  |1 1 0 0 0 0|x x| AFcode| IDI (last 3 digits)   |Prefix(octet 0)|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 4-7  |             Prefix (octets 1 through 3)       | Area (octet 0)|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 8-11 | Area (octet 1)|    ID (octets 0 through 2)                    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 12-15|       ID (octets 3 through 5)                 |   NSEL        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



 The AFcode is 1111 (hexadecimal F) to represent AFI code 39 (DCC, digital
 country code). Otherwise, AFI code 47 (ICD, international code
 designator) is implicit and AFcode is the first digit of the ICD.

 The longest CLNP prefixes in use today appear to be 4 octets, in
 NORDUNET (the Nordic academic network). Thus the semantics of existing
 20-octet NSAPAs are fully mapped. DECnet/OSI address semantics are also
 fully mapped.

 The NSEL octet is retained. It is of no use for TCP and UDP traffic,
 but would be of use if a future revision of CLNP used the same format.
 The alignment is similar to that for 20-octet NSAPAs.


2. 16-byte IPng addresses inside a 20-octet NSAPA

 The main goal of this embedding is to allow CLNP packets that encapsulate
 IPng packets to be routed in a CLNP network using the IPng address
 architecture. An arbitrary number of bytes of the IPng address can be
 used as a CLNP routing prefix.

 The first three octets are an IDP meaning "this NSAPA embeds a
 16 byte IPng address" and the last octet is a dummy selector.
 Sorry about the alignment, but it seems very risky to overload
 the selector octet.

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 0-3  |  AFI = 47     |   ICD = ISoc (TBD)            | IPng (byte 0) |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 4-7  |             IPng (bytes 1-4)                                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 8-11 |             IPng (bytes 5-8)                                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 12-15|             IPng (bytes 9-12)                                 |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 16-19|       IPng (bytes 13-15)                      |  NSEL = dummy |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


---

Revised NSAPA mapping Brian Carpenter CERN-CN