Hello List, SIP and NAT - this issue has been raised on numerous occassions. I finally got a small working demo for SIP Instant Messaging through a NAT gateway (next on the list is to try it with some RTP traffic). I am using "siproxd" http://sourceforge.net/projects/siproxd on the NAT gateway. Siproxd is an proxy/masquerading daemon for the SIP protocol. It allows SIP clients to work behind an IP masquerading firewall or router. Demo setup - [UA1] <------> [siproxd/NAT Gateway]<------->[SER]<------->[UA2] where UA1 is behind a NAT gateway, siproxd is running on the NAT gateway and UA2 is on the public side. Both UA1 and UA2 uses SER as the registration server in this demo (siproxd is also capable of working as a registration server). UA1 is configured to use siproxd as its outgoing proxy. All SIP packets going through siproxd are re-written to address the NAT traversal issues (so the SIP packets appear to be coming from the NAT gateway). I used Siemens SIP client for this demo. siproxd is also capable of proxying RTP traffic - although I am yet to test this feature. Many of us are looking for "siproxd" like utility that addressed the NAT traversal problems. And I think it will be a great idea to add such a capability to SER. In the meantime, it will be great if more people tests and contributes to siproxd. Thoughts anyone? Dhiraj Bhuyan Security Research Engineer BT Exact Tel: +44 1473 643932 Mob: +44 7962 012145 Email: dhiraj.2.bhuyan(a)bt.com