Hi all!

I'm still working on incorrect routing of ACKs/BYEs with certain conditions and asking for guru help.

My network looks like this:

192.168.4.218 -> TCP -> NAT (1.2.2.94) -> (1.2.0.160) Kamailio (1.2.0.160) -> UDP-> backend servers (1.2.2.44).

IP address 1.2.0.16 is a 1.2.0.160/32 on loopback interface lo, and it is announced via BGP to neighbours. There is also 1.2.3.46/30, which is used to maintain BGP session.

Backends are Asterisk 11 machines with "outboundproxy" sip peer setting set to Kamailio address. Kamailio forwards registrations to Asterisk servers with authentication and caches successful attempts to its internal DB. Natted clients are managed adding 'received' param to reg contact. When backend calls client, Kamailio takes correct URI from 'received' and forwards request.

There is a possibility Kamailio will have several IP addresses for outbound clients. To specify source address of forwarded packets I set $fs. For initial requests and responses all works fine, but there are troubles when dealing with ACKs and BYEs.

In case I don't specify interfaces with 'listen' , Kamailio listens on 1.2.0.160 and 1.2.3.46. I use $fs to set 1.2.0.160 as outgoing interface, and it works for requests. But when Kamailio forwards ACKs and BYEs, it uses 3.46 instead of 1.2.0.160, especially in case of TCP client and UDP backend.

If I set mhomed = 0 and specify Kamailio to listen only to 1.2.0.160, everything works fine, except UDP <-> TCP signalling conversion. When natted TCP client receives call from backend, it answers with 200 OK and ACK from backend is never back to client. At the same time UDP<->UDP works fine.

I've noted that TCP and UDP ACKs differ in Record-route headers, in case of TCP there are two records of Kamailio UDP/TCP. I have enable_double_rr = 1.

UDP ACK: ACK sip:0097242@192.168.4.218:5063 SIP/2.0. Via: SIP/2.0/UDP 1.2.2.44:5060;branch=z9hG4bK31d1a26c;rport. Route: sip:1.2.0.160;lr=on;ftag=as7af34000. Max-Forwards: 70. From: sip:8121230000@1.2.2.44;tag=as7af34000. To: sip:0097242@192.168.4.218:5063;received=sip:1.2.2.94:64825;tag=3122411720. Contact: sip:8121230000@1.2.2.44:5060. Call-ID: 56c5362d2250df6777e6665523964729@1.2.2.44:5060. CSeq: 102 ACK. User-Agent: Zero vPBX. Content-Length: 0.

This ack forwarded to destination correctly (to external IP 1.2.2.94:64825). Actually, I don't understand why, because $du is null and no functions logged that rURI was modified...

TCP ACK: ACK sip:0097242@192.168.4.218:5062;transport=TCP SIP/2.0 Via: SIP/2.0/UDP 1.2.2.44:5060;branch=z9hG4bK08f7b9f2;rport Route: sip:1.2.0.160;r2=on;lr=on;ftag=as5cc06d60,sip:1.2.0.160;transport=tcp;r2=on;lr=on;ftag=as5cc06d60 Max-Forwards: 70 From: sip:8121230000@1.2.2.44;tag=as5cc06d60 To: sip:0097242@192.168.4.218:5062;transport=TCP;received=sip:1.2.2.94:57735;transport=TCP;tag=4089422268 Contact: sip:8121230000@1.2.2.44:5060 Call-ID: 3a72968b552bdb8875e3215431f1522d@1.2.2.44:5060 CSeq: 102 ACK User-Agent: Zero vPBX Content-Length: 0

This ack doesn't get forwarded anywhere, although Kamailio says:

DEBUG: <core> [forward.c:592]: forward_request(): Sending:#012ACK sip:0097242@192.168.4.218:5062;transport=TCP SIP/2.0#015#012Via: SIP/2.0/TCP 1.2.0.160;branch=z9hG4bK42a6.5e57399c6a2c1dae96f28c7381b6c64e.0#015#012Via: SIP/2.0/UDP 1.2.2.44:5060;received=1.2.2.44;branch=z9hG4bK26130626;rport=5060#015#012Max-Forwards: 69#015#012From: sip:8121230000@1.2.2.44;tag=as74c521ed#015#012To: sip:0097242@192.168.4.218:5062;transport=TCP;received=sip:1.2.2.94:65535;transport=TCP;tag=547751151#015#012Contact: sip:8121230000@1.2.2.44:5060#015#012Call-ID: 10dfa7d00a9848c411a28bb54edf0f14@1.2.2.44:5060#015#012CSeq: 102 ACK#015#012User-Agent: Zero vPBX#015#012Content-Length: 0#015#012#015#012.

So I'm trying to understand - how Kamailio get correct destination address to send to in case of UDP <-> UDP ack, and why the same doesn't work in case of TCP?

If I turn on mhomed = 1, it breaks forwarding of UDP ACKs too... Maybe it is because of 1.2.0.160/32 IP address it is placed on lo iface, or there should be some entries in IP routing table on Kamailio host allowing selection of 1.2.0.160?

Thanks in advance!