The strangest thing just started happening to me. My switch is colocated in a data center. Yesterday I installed an Adtran NetVanta 3430 router at my office. Another server on the network at the office is handing out DHCP to the phones. After a few minutes, when you 4-digit dial from one extension (behind the LAN)to another, the call rings to voicemail -- the other endpoint does not get an audible ring. And when you dial them from the IVR, you get the same thing. It seems like it takes about 2 minutes for the registration to fall off. Polycom phones. I put 120 in server.1.reg.expires at the recommendation of my reseller. Before it was blank. Then I moved the phones to a different office running a NetGear router that is handing out DHCP. Same thing happened. But in this case, it is a little different. After the two minutes, if you dial one phone and don't get an answer, and then dial out from that phone to the first phone, it seems to open the channels back up and you can 4-digit dial again until the time runs out. On my router that sits in front of my switch I am forwarding 5060 and 10K-20K UDP to the private address of my switch. I am not forwarding any 5060 or 10K-20K traffic on the endpoint LANs, but I am setting QoS to prioritize both. Any suggestions? Thanks.