[Users] TCP-alias and NAT - one more try to get an answer

Hi All, I just wanted to ask you once again about the TCP-alias riddle. I found out, that there is a problem with the combination of fix_nated_contact(), force_tcp_alias() and NAT: Imagine following situation: Alice behind NAT: socket 172.16.0.6:2421 Nat-Box translates this to 192.168.0.13:6007 The Outbound-Proxy of Alice is 192.168.0.1 Bob is registered with 192.168.1.1 1.) Her INVITE: ==================================================================== INVITE sip:bob@192.168.1.1:2331;transport=tcp;line=wxqurd1s SIP/2.0 [...] Via: SIP/2.0/TCP 172.16.0.6:2421;received=192.168.0.13; branch=z9hG4bK-wm9jcstcboys;rport=6007 From: "Alice" <sip:alice@atlanta.com>;tag=sufzmxi0us To: "Bob" <sip:bob@biloxi.com>;tag=c9550czwtn [...] Contact: <sip:alice@172.16.0.6:2421;transport=tcp;line=fyyuh6tl> [...] ==================================================================== 2.) fix_nated_contact() doesn't work with TCP (look at nathelper.c). force_tcp_alias() now creates following tuple as TCP-alias: 192.168.0.13:6007 to 192.168.0.13:2421 Reason: The TCP-alias is not built solely from the Via-header as suggested in the draft. The portnumber is taken from the Via-header and the IP-address is taken from the source of the incoming datagram. I read it in the sourcecode and assured it by contacting Andrei! 3.) So as a result of the notfixed Contact-header of Alice's INVITE the BYE of Bob is addressed to 172.16.0.6:2421. But no TCP-alias exists for this socket :-( 4.) I made following test by rewriting the Contact-header.... ==================================================================== if (method=="INVITE") { replace("Contact: <sip:alice@172.16.0.6:2421;transport=tcp;", "Contact: <sip:alice@192.168.0.13:2421;transport=tcp;"); } ==================================================================== ...with success. Now TCP-alias works as you can see on my Ethereal-trace below! Compare the destination port of the packet to the destination port of the RURI! ==================================================================== [...] Transmission Control Protocol, Src Port: 5060 (5060), Dst Port: 6007 (6007), ... Session Initiation Protocol Request-Line: BYE sip:alice@192.168.0.13:2421;transport=tcp;line=fyyuh6tl SIP/2.0 Message Header [...] From: "Bob" <sip:bob@biloxi.com>;tag=kcsveifugd To: "Alice" <sip:alice@atlanta.com>;tag=ricaq5cy15 Contact: <sip:bob@192.168.1.1:2331;transport=tcp;line=wxqurd1s> [...] ==================================================================== Another solution: Comment the lines in nathelper.c which force the return in case of TCP or TLS. Now all works well! But why?????????????? regards, Philipp