AT&T CallVantge and D-Link DVG-1120M Help

Rich Tehrani : Communications and Technology Blog -
Rich Tehrani
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AT&T CallVantge and D-Link DVG-1120M Help

I received this rather detailed e-mail on configuring hardware for AT&T CallVantage. Havent tested this myself but it looks important enough to pass along. This is likely the AT&T Callvantage article being referred to. Hello,

I just spent the entire day trying to figure out how to get port forwarding working on the DVG-1120M or a way to get it to work behind a firewall/router, i came across an article you posted on it a few months ago. I have found out several distressing facts about the DVG-1120M and AT&T's service that you might find interesting.

* Bad networking logic, when the 1120 connects it sends some information about its connection to at&t using an http form post method, part of the connection data that is sent is the 1120's WAN IP, most routers support NAT but none support filtering IP's out of http data thats just not done.. so AT&T only tries to send packets to the IP specified in that HTTP post (rather than the IP its recieving this data from, which would be logical) so it cant communicate to the 1120 unless the IP the unit has for its WAN port is publicly reachable and can be routed to the 1120. So thats why it doesn't work. And its been like this for over a year. They have been telling customer's "new products/updates should be rolling out in about a month" for over a year! They did update their firmware earlier this month but it seems to have broken port forwarding completely

* No port forwarding, yea port forwarding doesnt seem to work at all anymore, previously it worked on 6 single ports (no ranges) which was better than nothing i guess, now it appears to be able to forward many ports in the configuration, but none of them are actually forwarding

* No DMZ. DMZ to a router behind the 1120 would really be helpful, especially now that port forwarding doesnt work, but this feature is not available

* Crippled connection while phone is on, When you are on the phone line the 1120 practically shuts down other net traffic, outgoing traffic is greatly effected even if the outgoing bandwidth that the 1120 requires is only a fraction of your connections available outgoing bandwidth. If it were BEHIND another router it wouldnt be able to effect your whole network like this and the QoS of the calls would be virtually uneffected.

there are 2 ways to get a decent connection working with forwarded ports:

1. Set up the 1120 to use bridge mode (turn off nat, turn on bridged mode) this basicly keeps the 1120 out of your business, the problem is you need more than one public IP from your ISP for it to work

2. use Two routers(but this requires a static IP) and connect one(lets say Router1) directly to your ISP (its WAN would be from your ISP, lets say and for its LAN have some private IPs (like 192.168.1.x) and then connect Router2 upto router1 (its WAN will be 192.168.1.x and its LAN will be (65.65.65.x) then connect the 1120 last and set its WAN ip to be! This way the 1120's WAN port as far as it knows is and that address gets put into the HTTP POST data, the packet sent is translated twice (back into though before going out!) AT&T recieves the packet with in it and tries to use that address to connect. Lastly you need to set the DMZ for Router1 to Router2, and the DMZ on Router2 to the 1120 so packets can get back (or set up a static route) It might be possible to do with 1 router too but im not having any luck on mine.

Anyway i thought this info might be useful or interesting to you and i just spent all day/night figuring this all out the hard way, tried lots of different configurations, read stuff all over the net (including your article) and even did packet logging on the 1120's output and I wanted someone else besides me to know this stuff so it feels like less of a waste of time ;)

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