Subject: [Sigtran] Bundling ABORT chunk with OOTB SHUTDOWN-ACK chunk in SCTP

From: Prasanna Kumar <[email-masked]>
Date: Tue, 20 Oct 2009 12:42:49 +0530

Hi,

For the OOTB packet handling in SCTP RFC 4960 says that, if SCTP
receives SHUTDOWN-ACK chunk as a OOTB chunk, it should send an
SHUTDOWN-COMPLETE chunk with the T-Bit set and copying the V-Tag of
the SHUTDOWN-ACK chunk. In RFC 4960 section 8.4:
5) If the packet contains a SHUTDOWN ACK chunk, the receiver should
respond to the sender of the OOTB packet with a SHUTDOWN COMPLETE.
When sending the SHUTDOWN COMPLETE, the receiver of the OOTB packet
must fill in the Verification Tag field of the outbound packet with
the Verification Tag received in the SHUTDOWN ACK and set the T bit in
the Chunk Flags to indicate that the Verification Tag is reflected.

As the ABORT chunk can be bundled with control chunks, in a scenario
where the SCTP is received the SHUTDOWN-ACK chunk bundled with the
ABORT chunk and SHUTDOWN-ACK is placed first. In the same section of
handling OOTB chunks, it says that the SCTP should discard the OOTB
packet containing the ABORT chunk. In RFC 4960 section 8.4:
2)  If the OOTB packet contains an ABORT chunk, the receiver MUST
silently discard the OOTB packet and take no further action.

Here what should be the expected behavior of the SCTP? Is it has to
reply to the SHUTDOWN-ACK with the SHUTDOWN-COMPLETE or it should
silently discard the packet? If it needs to be discarded, then its an
overhead on performance as SCTP needs to traverse through the all
chunks to detect the presence of the ABORT chunk in a packet.

Please let me know the expected behavior in this scenario and thanks in advance.

--
Regards,
Prasanna.

---

From: Aditya Sehgal <[email-masked]>
Date: Tue, 20 Oct 2009 14:43:46 +0530

Prasanna,
Section 9.1 of RFC 4960 also mentions that "an endpoint MUST NOT respond to
any received packet that contains an ABORT chunk"

Further, In section 8.4, points 3 onwards is an "else" portion of point 2
i.e. if the "oob" packet contains an ABORT chunk discard it else do point 3
onwards.

So, an "oob" blue packet containing an ABORT chunk must be discarded. You
will only have to traverse the whole chunks in case you receive an "oob"
packet which should impact the performance minimally.

Regards,
Aditya Sehgal

On Tue, Oct 20, 2009 at 12:42 PM, Prasanna Kumar <[email-masked]>wrote:

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