Subject: Re: Loop detection in Invite request in stateless proxy

From: Jonathan Rosenberg <[email-masked]>
Date: Wed, 01 Mar 2000 01:09:02 -0500

Benny Prijono wrote:
> 
> Hi all,
> 
> Section 12.3.1 of the draft states that:
>   "To prevent loops, a server must check if its own address is
>    already contained in the Via header of the incoming request"
> 
> Section 6.44.1 states that a 482 (Loop Detected) response MUST be
> returned when a loop is detected.
> 
> And finally, section 12.3 (last statement) states that a stateless proxy
> forwards every request and response it received.
> 
> Based on these statements, I think this is the correct behaviour for
> stateless proxy:
> 1. When the loop is detected, the stateless proxy will reply
>    with 482 (Loop Detected).
> 2. The UAC then will send ACK.
> 3. Proxy will forward ACK to the UAS.
> 4. UAS will simply drop the ACK, maybe after complains loudly
>    about the invalid message.
> 
> If this is the correct behaviour, then I'd like to know if there are any
> ways to prevent the ACK to be received by the UAS.

No. If the stateless proxy responds to the request, its not being a
stateless proxy anymore. So, when it sends that 482, and receives an
ACK, it doesn't forward the ACK. The ACK is for it. Its a similar
problem to what happens when a proxy receives a request thats bad, and
sends a 400 response. In this case, its not really acting like a
stateless proxy for this request.

Remember, stateful/stateless proxies are logic entities, and which role
a real device takes can differ from request to request.

-Jonathan R.

-- 
Jonathan D. Rosenberg                       200 Executive Drive
Chief Scientist                             Suite 120 
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---

From: Benny Prijono <[email-masked]>
Date: Wed, 01 Mar 2000 13:44:32 +0000

Jonathan Rosenberg wrote:
-deleted.

> a real device takes can differ from request to request.

Ah, that's it!
Seems that although I've re-read the RFC at least 2-3 times, still I
missed this concept, badly.. ;)

Thanks.

-- 
cheers,
Bennylp

---

From: Jonathan Rosenberg <[email-masked]>
Date: Wed, 01 Mar 2000 18:25:17 -0500

> missed this concept, badly.. ;)

Its probably not easy to figure out from the spec. I've made a note to
clarify in the next version.

-Jonathan R.