[SR-Users] Order of record-route

[Dirk Teurlings - Signet B.V.]

Hi,

Looking at an issue with SIP-Cisco and a Barracuda firewall, I've come
across something I need to know more about.

The setup is as follows:
CLIENT -> KAMAILIO -> ASTERISK
CLIENT <- KAMAILIO <- ASTERISK

Client sends INVITE, Kamailio forwards to Asterisk, SIP 100 and SIP 183
are being sent and finally a 200 OK. We now expect the Client to send
back an ACK packet, but that never reaches us.

In this case the SIP 183 is the first packet that contains the full
record route of the path, the 200 OK contain the same record-routes being:

Record-Route:
<sip:192.168.0.200;r2=on;lr;ftag=12D1120C-1C4;did=4c8.9203;nat=yes>
Record-Route: <sip:1.2.3.4;r2=on;lr;ftag=12D1120C-1C4;did=4c8.9203;nat=yes>
Record-Route: <sip:4.3.2.1;r2=on;lr;did=4c8.3f471377>
Record-Route: <sip:10.0.0.101;r2=on;lr;did=4c8.3f471377>

192.168.0.200 is the private address of Kamailio
1.2.3.4 is the public address of Kamailio
4.3.2.1 is the public address of the Client
10.0.0.101 is some private addres of the Client

		
What we're seeing is that the Client is sending his ACK message to our
192.169.200 private address, which he will never reach. So me question
in this case is; is the order of the Record-route headers relevant and
do I have any say in which order Kamailio outputs these headers?

To be clear, the Kamailio config only contains one reference to
record_route which is caught for INVITE messages, which only fires when
all things like NAT and transaction checks haven't already picked it up.

Kind regards,
Dirk