IN MY NETWORK WHICH WAS WORKING FOR A LONG TIME HAS SUDDENLY A PROBLEM WHICH IS THE FAST ETHERNET PORT GOES DOWN AND AFTER A WHILE IT GOES UP AND SO ON, I DECIDED TO CHANGE THE ROUTER, THE SAME THING HAPPEN IN MY NETWORK, COULD YOU HELP?
Your router (assuming the FE is on a router) is probably not receiving the keepalives that are sent every 10s. This is likely due to a network or cabling problem and not a problem with the router itself.
Check what happens when you connect the fe to another switchport. It should stay up.
