i would like to know what could be root cause(s) that can make a single vlan got host flapping? in my case the router connection became very very slow even cannot be telneted due to high CPU utilization. a host with MAC address has made this router and access switch on the same vlan having connection issue. when the downlink from router disabled, it came back to normal.fiber has been verified okay. was this due to switch port? gbic?or spanning tree? need your advice here. thanks in advance.
Sounds like a broadcast storm was created. Host flap or mac-flap just means that the exact same mac-address was being written to 2 different ports at the same time. A user probably has a hub attached to your network and thought he could "double" his bandwidth by attaching two cat 5 cables to his hub. Or someone plugged a crossover cable between 2 ports on the same switch, both ports would have to have BPDU filter enabled on them for that to be an issue though.
Looks like a L2 loop.
You need to find which 2 port are looped and remove the cause of the loop from your network.