I was under the impression that the Cisco fixup protocols broke the SIP headers Klaus Darilion wrote:

Hi, Are you trying to traverse two NAT routers, or just your PIX? Personally, my home lab runs through two NAT (actually PAT) routers before getting to my OpenSer proxy on the Internet. The first router is the ActionTec MI-424 provided by my ISP. I read somewhere it has ALG for SIP and MGCP. Then I also have a Cisco 1760 to route between 4 internal VLAN subnets. Only a couple of these subnets (sub-interfaces) are configured for PAT, but they do employ both SIP and DNS ALG. Things appear to work fine. I have never tried STUN at the UA (would not expect it to work in my case anyway). The SIP ALG may be problematic if you do not REGISTER through them because this is where initial mappings occur. That aside, my perception is that the SIP ALG bugs have already been worked out. -will Jeremy McNamara wrote: