We have a customer that has one IP phone at a remote location (only one for now, more to be installed) that after about 12 hours it stops working, says something like server not found. When the routers are power cycled, the IP phone starts working again. Repeat problem. There is a VPN in place, separate from the customer's network. The routers are Cisco routers, about a month old. The customer's IT person says all ports are open and nothing is blocking the IP phone, no firewalls etc. When we bring the IP phone to the main site and connect it to the customer's LAN, no problems.

Has anyone come across this before? Solutions? Ideas? Any help is greatly appreciated. Thanks.