If I have Ser listening on two IP addresses it will forward a Invite from the address it received it on and not from the address the target registered at. This will cause a Nat problem as there will be no binding for that combination. In the example below Stephen is registered at xxx 162 and 888 at xxx 163 and both are behind the same Nat. A call is attempted in each direction. Is this the correct behavior? Source Destination Protocol Info 202.76.176.229 206.123.107.162 UDP Source port:5061 Destination port: 5060 202.76.176.229 206.123.107.163 SIP/SDP Request: INVITE sip:stephen@blablabla.com.au, with session description 206.123.107.163 202.76.176.229 SIP Status: 100 trying -- your call is important to us 206.123.107.163 202.76.176.229 SIP/SDP Request: INVITE sip:stephen@202.76.176.229:5061;user=phone, with session description 206.123.107.163 202.76.176.229 SIP/SDP Request: INVITE sip:stephen@202.76.176.229:5061;user=phone, with session description 206.123.107.163 202.76.176.229 SIP/SDP Request: INVITE sip:stephen@202.76.176.229:5061;user=phone, with session description 202.76.176.229 206.123.107.163 SIP Request: OPTIONS sip:sip.blablabla.com.au 206.123.107.163 202.76.176.229 SIP Status: 404 Not Found 206.123.107.163 202.76.176.229 SIP/SDP Request: INVITE sip:stephen@202.76.176.229:5061;user=phone, with session description 202.76.176.229 206.123.107.163 SIP Request: CANCEL sip:stephen@blablabla.com.au 206.123.107.163 202.76.176.229 SIP Status: 200 ok -- no more pending branches 206.123.107.163 202.76.176.229 SIP Status: 487 Request cancelled 202.76.176.229 206.123.107.163 SIP Request: ACK sip:stephen@blablabla.com.au 202.76.176.229 206.123.107.162 UDP Source port: 5061 Destination port: 5060 202.76.176.229 206.123.107.162 SIP/SDP Request: INVITE sip:888@blablabla.com.au;user=phone, with session description 206.123.107.162 202.76.176.229 SIP Status: 100 trying -- your call is important to us 206.123.107.162 202.76.176.229 SIP/SDP Request: INVITE sip:888@202.76.176.229:5060, with session description 206.123.107.162 202.76.176.229 SIP/SDP Request: INVITE sip:888@202.76.176.229:5060, with session description 206.123.107.162 202.76.176.229 SIP/SDP Request: INVITE sip:888@202.76.176.229:5060, with session description 206.123.107.162 202.76.176.229 SIP/SDP Request: INVITE sip:888@202.76.176.229:5060, with session description 202.76.176.229 206.123.107.162 SIP Request: CANCEL sip:888@blablabla.com.au;user=phone 206.123.107.162 202.76.176.229 SIP Status: 200 ok -- no more pending branches 206.123.107.162 202.76.176.229 SIP Status: 487 Request cancelled 202.76.176.229 206.123.107.162 SIP Request: ACK sip:888@blablabla.com.au;user=phone _______________________________________________ Serusers mailing list serusers(a)lists.iptel.org http://lists.iptel.org/mailman/listinfo/serusers