SER doesn't seem to be returning the Unauthorized message to the correct port, but it does get at least the right IP. You will notice the REGISTER is received on 216.43.27.75:56059 but the Unauthorized is sent back to 216.43.27.75:5060. Is there any way to get SER to send back to the correct port so symmetrical NAT will work correctly? U 216.43.27.75:56059 -> 198.88.216.87:5060 REGISTER sip:bwsys.net SIP/2.0..Via: SIP/2.0/UDP 192.168.1.119:5060;branch=z9hG4bK2309979991..From: SafeWayLine1 <sip:SafeWayLi ne1@bwsys.net>;tag=1023220770..To: SafeWayLine1 <sip:SafeWayLine1@bwsys.net>..Call-ID: 3966543944@192.168.1.119..CSeq: 15 REGIS TER..Contact: <sip:SafeWayLine1@192.168.1.119:5060>..max-forwards: 70..user-agent: Azacall200..expires: 60..Content-Length: 0.. .. # U 198.88.216.87:5060 -> 216.43.27.75:5060 SIP/2.0 401 Unauthorized..Via: SIP/2.0/UDP 192.168.1.119:5060;branch=z9hG4bK2309979991;received=216.43.27.75..From: SafeWayLine 1 <sip:SafeWayLine1@bwsys.net>;tag=1023220770..To: SafeWayLine1 <sip:SafeWayLine1@bwsys.net>;tag=ceb07c727e9d78dd71cafc9196e2f4 a7.535c..Call-ID: 3966543944@192.168.1.119..CSeq: 15 REGISTER..WWW-Authenticate: Digest realm="bwsys.net", nonce="416067d1a3983 6e4022698b6217bab605b990a18", qop="auth"..Server: Sip EXpress router (0.8.14 (i386/linux))..Content-Length: 0.... ---------------------------------------- Michael Shuler, C.E.O. BitWise Communications, Inc. (CLEC) And BitWise Systems, Inc. (ISP) 682 High Point Lane East Peoria, IL 61611 Office: (217) 585-0357 Cell: (309) 657-6365 Fax: (309) 213-3500 E-Mail: mike(a)bwsys.net Customer Service: (877) 976-0711