Hello I'll post the answers to the two replies:

Andrei> Do you have another UA behind the same nat, using 5060?

No it's only 1 Phone ---- ADSLRouter(NAT) ------- Internet ---------- Ser

Dhiraj > ..i'l post the two ngreps again: I'm sorry for the long post. What I can see is, when ser runs on port 5070 the register contains a private ip in the 'Via:' header. When it runs on 5060 The 'Via:' header contains the public IP of the router and an unprivileged port.

----------------------------------------------- 5070 ----------------------------------------------- filter: ip and ( port 5070 ) # U 213.219.137.137:5070 -> 212.71.0.60:5070 REGISTER sip:ser.edpnet.net:5070 SIP/2.0. Via: SIP/2.0/UDP 10.0.0.2:5070. Supported: replaces. User-Agent: SIP201 (lp201sip.100a). Contact: sip:bart@10.0.0.2:5070;expires=60. From: sip:bart@ser.edpnet.net ;tag=a000002-13ce-0-42e-7fea. To: sip:bart@ser.edpnet.net. Call-ID: a000002-13ce-0-406-79bf-1. CSeq: 1 REGISTER. Content-Length:0. .

# U 212.71.0.60:5070 -> 213.219.137.137:5070 SIP/2.0 401 Unauthorized. Via: SIP/2.0/UDP 10.0.0.2:5070;rport=5070;received=213.219.137.137. From: sip:bart@ser.edpnet.net ;tag=a000002-13ce-0-42e-7fea. To: sip:bart@ser.edpnet.net;tag=2497a39c629b119dac83769f58cd2b29.1cd2. Call-ID: a000002-13ce-0-406-79bf-1. CSeq: 1 REGISTER. WWW-Authenticate: Digest realm="ser.edpnet.net", nonce="40fcce4ec4ab3796c95cb2c87a9d94a05651ed08". Server: Sip EXpress router (0.8.13-dev-33-usrloc (i386/linux)). Content-Length: 0. Warning: 392 212.71.0.60:5070 "Noisy feedback tells: pid=18743 req_src_ip=213.219.137.137 req_src_port=5070 in_uri=sip:ser.edpnet.net:5070 out_uri=sip:ser.edpnet.net:5070 via_cnt==1". .

# U 213.219.137.137:5070 -> 212.71.0.60:5070 REGISTER sip:ser.edpnet.net:5070 SIP/2.0. Via: SIP/2.0/UDP 10.0.0.2:5070. Supported: replaces. User-Agent: SIP201 (lp201sip.100a). Contact: sip:bart@10.0.0.2:5070;expires=60. Authorization: Digest username="bart", realm="ser.edpnet.net", nonce="40fcce4ec4ab3796c95cb2c87a9d94a05651ed08", uri="sip:ser.edpnet.net:5070", response="ea0329c8f3a4d199230733feb750d3a1", algorithm=MD5. From: sip:bart@ser.edpnet.net ;tag=a000002-13ce-40fccd8d-1991-7051. To: sip:bart@ser.edpnet.net. Call-ID: a000002-13ce-0-406-79bf-1. CSeq: 2 REGISTER. Content-Length:0. .

# U 212.71.0.60:5070 -> 213.219.137.137:5070 SIP/2.0 200 OK. Via: SIP/2.0/UDP 10.0.0.2:5070;rport=5070;received=213.219.137.137. From: sip:bart@ser.edpnet.net ;tag=a000002-13ce-40fccd8d-1991-7051. To: sip:bart@ser.edpnet.net;tag=2497a39c629b119dac83769f58cd2b29.1cd2. Call-ID: a000002-13ce-0-406-79bf-1. CSeq: 2 REGISTER. Contact: sip:bart@213.219.137.137:5070;expires=60. Server: Sip EXpress router (0.8.13-dev-33-usrloc (i386/linux)). Content-Length: 0. Warning: 392 212.71.0.60:5070 "Noisy feedback tells: pid=18743 req_src_ip=213.219.137.137 req_src_port=5070 in_uri=sip:ser.edpnet.net:5070 out_uri=sip:ser.edpnet.net:5070 via_cnt==1". .

----------------------------------------------- 5060 ----------------------------------------------- filter: ip and ( port 5060 ) # U 213.219.137.137:5060 -> 212.71.0.60:5060 REGISTER sip:ser.edpnet.net:5060 SIP/2.0. Via: SIP/2.0/UDP 213.219.137.137:47726. Supported: replaces. User-Agent: SIP201 (lp201sip.100a). Contact: sip:bart@10.0.0.2:5060;expires=60. From: sip:bart@ser.edpnet.net ;tag=a000002-13c4-0-429-495. To: sip:bart@ser.edpnet.net. Call-ID: a000002-13c4-0-401-719e-1. CSeq: 1 REGISTER. Content-Length:0. .

# U 212.71.0.60:5060 -> 213.219.137.137:5060 SIP/2.0 401 Unauthorized. Via: SIP/2.0/UDP 213.219.137.137:47726;rport=5060. From: sip:bart@ser.edpnet.net ;tag=a000002-13c4-0-429-495. To: sip:bart@ser.edpnet.net;tag=61a88e7fd5f0561d96cde0cc9ecba6d7.2508. Call-ID: a000002-13c4-0-401-719e-1. CSeq: 1 REGISTER. WWW-Authenticate: Digest realm="ser.edpnet.net", nonce="40fcccbe3b4e06bc429de0a886d7b43409cb8427". Server: Sip EXpress router (0.8.13-dev-33-usrloc (i386/linux)). Content-Length: 0. Warning: 392 212.71.0.60:5060 "Noisy feedback tells: pid=18727 req_src_ip=213.219.137.137 req_src_port=5060 in_uri=sip:ser.edpnet.net:5060 out_uri=sip:ser.edpnet.net:5060 via_cnt==1".