[cisco-voip] VOIP phones failing to set up

[Joseph Mays]

As described, I have the problem of having Cisco 7960 phones that will set 
up fine with call manager running on a cisco 3640 on our network. We are 
using SCCP. I have now determined that the phones set up fine no matter 
where you place them on our network, except when they are at the end of one 
of our DSL lines. The phones connect to the call manager, download their 
configs via TFTP, then reset and go through the process again. Put them 
anywhere but down a DSL line and they register with the call manager and 
complete setup fine.

An item of note is that the T1 lines, which they work fine on, and the DSL 
lines terminate on the same cisco 7206. So whatever is keeping them from 
working is either something on the 7206 specifically relating to the DSL 
lines, or something on the lines themselves.

Curiouser still, I have gotten them to set up fine at the end of the DSL 
lines IF they are set up behind another router doing DHCP and NAT, with a 
private IP address.

What I need to know now is some idea where to look to isolate the problem 
further. Am I correct in assuming that ports 2000 and 16384-32767 need to be 
open down the DSL lines? I have them opened, as near as I can tell, but if 
any of those are closed would it cause this problem?