(Sorry for cross-posting from Sip-Implementors; however, upon some reflection this is really more of a Kamailio mechanics question.) Greetings, I have a scenario where endpoint A is calling endpoint B through proxy P. Endpoints A and B are on different networks that are not directly reachable--A is on the public Internet, to which proxy P is connected, but NAT'd, and B is on a private RFC1918 network on which the proxy P has an interface as well. The purpose of proxy P is to make calling A <-> B possible, while providing the appropriate far-end NAT traversal functionality for A and so on and so on. It does this by inserting the correct Record-Route headers into the INVITE from A, and otherwise by staying in the signaling path; both A and B can reach the proxy, so all requests and replies go through it. The problem I'm having is prior to full dialog establishment. Upon receipt of INVITE from A by way of proxy P, B replies with 183 + SDP and also: Require: 100rel In the 183 it provides a Contact on its private network that A obviously cannot reach: Contact: <sip:xxxxx@192.168.0.10:5060> As a result, A attempts to send PRACKs to sip:xxxxx@192.168.0.10, which are obviously not going to go anywhere. After not receiving a few of these expected PRACKs, B replies to the call with a final negative failure. The question is, is there anything I can twiddle on the proxy to make this work? The problem with PRACKs is that although they are sequential requests, they arise (in this case) prior to the point at which RR can be used to guide them through the proxy. The most obvious answer is, "Make B not Require: 100rel", of course. However, that is not an option here. Thanks! -- Alex Balashov - Principal Evariste Systems LLC 260 Peachtree Street NW Suite 2200 Atlanta, GA 30303 Tel: +1-678-954-0670 Fax: +1-404-961-1892 Web: http://www.evaristesys.com/