strange problem on cisco catalyst 3560 switch

[holdahl]

This strange problem has occurred a few times on some of our catalyst 3560 switches: we are using desktops of different models as client computers. On a few of our switches some computers are suddenly denied access to the network. It seems like the switch denies that mac address no matter what port it is plugged into. When I try to plug it into another switch in the stack it works fine. When I change the mac address on the 'problem' computer it works fine again on the 'problem' switch. Has anyone had this problem or got any suggestions on what may cause this?

 

[ADB100]

I change the mac address on the 'problem' computer it works fine again on the 'problem' switch

Are you saying you change the MAC addresses on machines by default?

Andy

 

[holdahl]

No. I said that when I tried to the change the mac-address (NIC) on that computer, I got connection to network on that switch. The changing of mac-address was just to see if the problem was solved.

 

[ADB100]

OK. Do you use port security and/or IP Phones? How are the switches connected together and is it layer-3 (routed) or just layer-2 (flat)? What error messages are logged on the switch when a PC looses network connectivity? It may be worth posting some configuration captures - global spanning-tree section and then some sample user ports and maybe your inter-switch links.

Andy