I am currently trying to get the following scenario to work.
Warning: I am a software engineer--not a network admin.
I have various SIP endpoints (sip based video servers) on a LAN. On a Windows Server on that LAN, I have tekSIP running as the SIP Registrar. All of this works so far. I can register from the endpoints with the registrar and make calls just fine.
Now I want to allow remote calls from outside our LAN. First, I put an A entry in our dns: "sip" which resolves to our external ip. I setup an SRV record for _sip._udp.sip.ourdomain.com. If I ping sip.ourdomain.com, everything works, the dns resolves to our public ip and the ping works. Everything also looks good in nslookup.
On our router, I forwarded port 5060 for udp to the server running tekSIP. Here is where the problem comes in. If I try to register or make a call from a remote endpoint, it always fails, and I can't even see the incoming request in wireshark on the application server.
Any ideas? I would be happy to post any config files you request.