Our network exists of two core switches 4500 in hsrp and a couple of access switches 3750's and 3550's. On one side clients complain of connectivity loss, if i do a ping I see somethimes time outs. I checked errors on the ports and the logfile without any result. The uplink to the access switch is a port-channel with just one port in it. What I discovered during this timeout is that the mac-address can't be found on the coreswitch. At the end I have found the mac-address on an other access-switch, so on a switch were host WASN't attached. When i reissued the command (sh mac-add....) the mac-address was gone ??