DMZ troubleshooting

I am using a DDWRT router. I have a SIP phone system in the DMZ of the router. I can call out, but cannot receive calls. The packet capture on the SIP server, shows "error 404 - forbidden" when the number is called. To test, I went to a website that checks for open ports, and told it to check for the port I am using, on my WAN address. Port is reported closed. Being the port i am querying, is actually on a device behind the WAN address, and that port is not really being forwarded to the device, however the device is in the DMZ, is that the expected behavior? How to test, if that port can be reached from the outside.
GCITechAsked:
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Jan SpringerCommented:
Are you not port forwarding from the outside to the IP on the DMZ for that/those ports?
GCITechAuthor Commented:
I am not forwarding any ports, as I thought if the device was in the DMZ, it was exposed to all ports. Is that not how it works?
Jan SpringerCommented:
No.  The DMZ is the zone that is less secure than than your internal zone but is inside your network.
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Brian MurphyIT ArchitectCommented:
You have a split-DNS scenario.  SIP address is useless outside your internal DNS resolution.

You need something external that points to another IP. It can be your ISP IP for all I care, just make sure that forwards to the same SIP IP that you set internal?

Make sense?

Pretty straight forward.

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Jan SpringerCommented:
If the SIP server is external and is not from an internal domain, split-DNS is not the problem.

Either way, he needs to allow the SIP server to originate a connection to his phone by forwarding those ports to the IP in the DMZ.
GCITechAuthor Commented:
split dns settings are probably taken care of in NAT settings portion of the phone server, and that is why it resolved the issue. Thanks..
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