Subject: [Sip] Re: [Sip-implementors] Loop detection & Via's branch

From: Jiri Kuthan <[email-masked]>
Date: Wed, 24 Jul 2002 10:23:23 +0200

Indeed. Using previous branch in calculating next branch
disables loop detection. Sounds like a spec inconsistency.

-Jiri

(moved to SIP mailing list)

At 09:47 AM 7/24/2002, Sachin Shenoy wrote:
>Hi,
>
>In RFC 3261 [16.6 (8)] it says that, for loop detection at proxy, 
>we should calculate the branch using top most Via header also. 
>I guess while using top-most Via header we should avoid using the branch. If branch is also used, the loop can go undetected as 
>the branch could be unique, even when the request has looped.
>(8.1.1.7 Says branch has to be unique across space and time).
>
>Hope I got it right. If I have missed anything please let me
>know.
>
>Thanks
>Sachin
>
>
>16.6 (8)
>"This is to ensure that if the
>request is routed back to the proxy and one of those fields
>changes, it is treated as a spiral and not a loop (see Section
>16.3).  A common way to create this value is to compute a
>cryptographic hash of the To tag, From tag, Call-ID header
>field, the Request-URI of the request received (before
>translation), *the topmost Via header*, and the sequence number
>from the CSeq header field, in addition to any Proxy-Require
>and Proxy-Authorization header fields that may be present." 

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