Nat confusion

Can anyone help me with this.

If I plug my Cisco 7940 into a network with a no-name router, calls can be made and recieved just fine.

If I try the same with a asterisk box, the register command in sip.conf will fail. I don’t have the option of opening 5060 on the no-name router

With a Cisco router, I can resolve this by opening 5060.

So how is the 7940 able to traverse the firwall and not *?

How I think it’s doing it, is by using the proxy setting, and going out via port 5065.

How can I achieve this with *, anyone?

Relevent sections of 7940 config that works

Proxy Server

proxy1_address: “”; Can be dotted IP or FQDN

Proxy Server Port (default - 5060)

proxy1_port: 5060

Outbound Proxy Support

outbound_proxy: “” ; restricted to dotted IP or DNS A record only
outbound_proxy_port: 5065 ; default is 5060