I'm running a Cisco 871 router in a LAN WAN setup. Nat, site-to-site VPN, Firewalling, etc. The problem is that the router stops forwarding traffic at random. The only way to fix this issue is to reboot the router using the console / powerswitch. Symptoms are as following:

• Router response times suddenly go through the roof (up to 1000 msec) until, after a few minutes, the router becomes totally unresponsive.
• After the router crashes, it cannot be pinged at all.
• When I connect a console cable to the router, I can use it like normal.
  • show proc cpu hist -> normal cpu load.
  • counters on interfaces do not increment.
  • logging does not show any strange output.
  • shut/no shut on an interface has no success
  • ping from the router to another device does not work.

I've tried several advsecurity IOS versions, 124-15T 124-24T. All the versions have the same symptoms.

Anyone any idea?