I found that my C4507 switch has received huge of HOSTFLAPPING with the prefix 0C:CC:01 & 0C:CC:01 :C4507#show log1378604: Mar 27 18:30:01.959 : %C4K_EBM-4-HOSTFLAPPING: Host 0C:CC:01:00:0C:CC in vlan 10 is flapping between port Gi5/1 and port Gi5/21...