Subject: [Tsvwg] Chunk and parameter Id conflict

From: "Khan, Mohammad" <[email-masked]>
Date: Thu, 21 Mar 2002 02:40:25 -0800

Hi All,
In the draft for Dynamic Ip modification
http://www.ietf.org/internet-drafts/draft-ietf-tsvwg-addip-sctp-04.txt two
new chunks have been introduced as ASCONF and ASCONF-ACK with chunktypes as
0xc1 and 0x80 respectivily. As per the RFC 2960 first two bits of the chunk
types specify the action to be taken when the chunk type is unspecified. So
following confusion in the chunk Ids would be observed.

	ChunkType	ChunkId		ChunkId with two MSBs
Observation
	ASCONF	0xc1		
	INIT		0x01		0xc1(Both the MSBs Set)	It matches
with ASCONF Chunk Type
	ASCONF-ACK	0x80
	DATA		0x00		0x80(One MSB set)		It
matches with ASCONF-ACK Chunk Type

As per the SCTP Implementors Guide
http://www.ietf.org/internet-drafts/draft-ietf-tsvwg-sctpimpguide-03.txt
2.4.2 - e "Each parameter type must be unique across all chunks". In the
draft
http://www.ietf.org/internet-drafts/draft-ietf-tsvwg-addip-sctp-04.txt six
new parameters have been added few of  which does not contain unique
parameter types considering the existing parameter types with two of the
MSBs set to specify action when peer does not recognize it. Following are
the observation.

	Parameter Type		ParameterId	ParameterId with twoMSBs
Observation
	IPV4 Address		0x0005		0xC005(Both MSBs set)
	Success report		0xC005
It matches with IPV4 address when two
msbs are set
	IPV6 address		0x0006		0xC006(Both MSBs set)
	Adaptation Layer Indication 0xC006
It matches with IPV6 address when two
	
msbs are set

Please comment.

Regards
kashif

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---

From: Andreas Jungmaier <[email-masked]>
Date: Thu, 21 Mar 2002 15:43:29 +0100

Kashif,

I think you mis-understand something here. 
There is absolutely no confusion at all. The RFC tells you
what you should do, if your implementation does not understand
a chunk type or a parameter type.
The rule in the RFC states that...
- ------------------ quote from RFC 2960 ----------------------------------
" Chunk Types are encoded such that the highest-order two bits specify
  the action that must be taken if the processing endpoint does not
  recognize the Chunk Type.
  00 - Stop processing this SCTP packet and discard it, do not process
       any further chunks within it.
  01 - Stop processing this SCTP packet and discard it, do not process
       any further chunks within it, and report the unrecognized
       parameter in an 'Unrecognized Parameter Type' (in either an
       ERROR or in the INIT ACK).
  10 - Skip this chunk and continue processing.
  11 - Skip this chunk and continue processing, but report in an ERROR
       Chunk using the 'Unrecognized Chunk Type' cause of error."
- ------------------ end quote from RFC 2960 ----------------------------------
...and...
- ------------------ quote from RFC 2960 ----------------------------------
" The Parameter Types are encoded such that the highest-order two bits
  specify the action that must be taken if the processing endpoint does
  not recognize the Parameter Type.
  00 - Stop processing this SCTP packet and discard it, do not process
       any further chunks within it.
  01 - Stop processing this SCTP packet and discard it, do not process
       any further chunks within it, and report the unrecognized
       parameter in an 'Unrecognized Parameter Type' (in either an
       ERROR or in the INIT ACK).
  10 - Skip this parameter and continue processing.
  11 - Skip this parameter and continue processing but report the
       unrecognized parameter in an 'Unrecognized Parameter Type' (in
       either an ERROR or in the INIT ACK)."
- ------------------ end quote from RFC 2960 ----------------------------------
Now, in your chunk processing there should be a routine that checks
whether you support a chunk (or parameter) that has been received,
and take the appropriate action, if your implementation does not.
The identifiers are unique, and only used for one chunk.

Best regards,
Andreas

> It matches with IPV6 address when two

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