[Freeswitch-users] Wrong IP on ACK?

Iñaki Baz Castillo ibc at aliax.net
Wed Nov 19 06:23:26 PST 2008

2008/11/19 David Aldworth <daldworth at teliax.com>:

> We're still having a problem with this. As you can see from the below the
> ACK goes to the port in the Contact field of the 200 OK instead of that of
> the UDP header, which is where their router is expecting to get the call
> from.

The ACK for a 200 OK (INVITE) is an in-dialog request, so it must be
sent to the SIP URI in the top most "Route" header (if there is a
proxy in the patch that added it during the INVITE) or to the SIP URI
indicated in the "Contact" of the 200 OK.
This is the right behaviour according to the SIP specs.

In your case, the 200 OK sent by Asterisk is:

U 2008/11/06 10:46:01.932294 ->
SIP/2.0 200 OK.
Via: SIP/2.0/UDP;branch=z9hG4bKU7360cS96r7Sg;received=;rport=5060.
User-Agent: Asterisk PBX.
Contact: <sip:317376XXXX at>.

Note that the Contact says no port, so it means default SIP port => 5060.
But note that the response comes from port 50085, why? it makes no
sense, but it's not a problem in FS but in your environment or your

Could you show us the INVITE sent from FS to Asterisk (including also
the real sourde/destination address). Is that IVITE sent to port 50085
or to port 5060 of Asterisk? Is there NAT somewhere between FS and
Asterisk in this scenario?

Iñaki Baz Castillo
<ibc at aliax.net>

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