Subject: [ANCP] A problem with the GSMPv3 state machine

From: Tom Taylor <[email-masked]>
Date: Tue, 12 Apr 2011 18:10:37 -0400

Actually, there are a couple of problems, but I've imposed a solution 
for one of them. The one I'm concerned about has to do with a case where 
the NAS proposes a Partition ID value in a SYN message (PType=1 and 
Partition ID is non-zero). Section 11.3 of RFC 3292 indicates that the 
AN can reject this (e.g., because that partition number is already 
assigned) by sending an RSTACK with non-zero values of PType and 
Partition ID -- for example, by copying these fields from the SYN.

The problem arises because, having sent the SYN, the NAS may enter 
SYNSENT state if it hasn't received a SYN in turn. According to the 
instructions for handling a packet arrival event in section 11.2, 
RSTACKs are ignored in SYNSENT state.

I think the solution is that instead of sending an RSTACK, the AN sends 
a SYN of its own if it hasn't already, either denying the use of 
partitions (PType=0) or assigning a different partition number (PType=2).

Is there ever an occasion where the NAS instead of the AN would find a 
particular Partition ID value unacceptable?

Tom Taylor

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From: Wojciech Dec <[email-masked]>
Date: Fri, 22 Apr 2011 11:30:40 +0200

> particular Partition ID value unacceptable?

I suppose a case for that would be should a single AN attempt to set-up
multiple ANCP adjacencies with the same NAS all using the same partition-id.

-Woj.
> 
> Tom Taylor
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