I just connected a new Juniper SSG550 firewall to a new GB interface (with "T" media ) on my 3845 router, and noticed that the link would go down after 20 minutes. Oddly the link showed still up according to the status, but I couldn't get to the Juniper connected... the ARP entry was stale. Clearing the ARP cache would bring the link back up and all was fine...for another 20 minutes, then it would "de-ARP(?)" again.
I found a work around by setting the ARP timeout on the new GB interface to 30 seconds. This works, but it is the only interface that I've had to do it with. I have other GB interfaces, but they are running at 100MB and show no trouble with the default timeout of 4 hours.
So is there some weird standard that says 1000-base-T has a limit of 20 minutes for ARP reliability? Am I going crazy?
Can someone explain this.