[OpenSIPS-Users] Trouble accepting an ACK to 200-OK with a bad rUri

Shawn Smith shawn at pinger.com
Wed Mar 16 18:55:35 CET 2011

I'm looking for suggestions on how to create a server-side workaround for an issue I'm getting in the field where the ALG logic in certain customer routers is putting bad data into the contact of a 200-OK message causing the resulting ACK back to the server to have the wrong rURI on it.

Here is an example of the content in the bad-ACK:

 Request-Line: ACK sip:5000 at 192.X.X.X:45219;transport=udp SIP/2.0
 To: <sip:5000 at 206.Y.Y.Y>;tag=vtK3jeZ4yQmmF
 From: "805ZZZZZ" <sip:805ZZZZZ at 206.Y.Y.Y>
 Route: <sip:206.Y.Y.Y;lr=on;did=c27.9ebcc7c7>
 Via: SIP/2.0/UDP 96.A.B.C:45219;branch=z9hG4bKiZKdxRM8VrEaYoN8;rport

I've sanitized the addresses.  206.Y.Y.Y is the address of the openSIPS server.  192.X.X.X is the bogus NAT'd address which the ALG modified 200-OK caused to be placed in the ACK.

With a standard-issue openSIPS config, the above ACK is given to loose_route() and then route(1), which decides it should be forwarded to the 192.X.X.X address - it's relayed to that (bogus) IP, and since the ACK never gets processed openSIPS keeps sending retries of the 200-OK, eventually giving up and tearing down the call.

I can easily detect this problem by seeing that the To: domain doesn't match the rURI.

I've tried setting modparam("tm", "ruri_matching", 0).  That has no effect.

I've modified the config to examine all ACK's for the above issue, and set $rd = $td before calling loose_route() in hopes that this would convince the dialog to accept the ACK and advance to the established state.  This seems like it should work, and I see the ACC module saying the 200 request was acknowledged.  But then openSIPS continues sending out 200-OK retries and the call is eventually torn down.

I'm looking for advice.  I need a server side workaround for this - I can't do it in the client.  What can I do in the openSIPS config to get the dialog to accept these mangled ACK's to the 200-OK and let the call move to established.

Thanks in advance for any help.

   -Shawn Smith
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