Question : Problem: Cisco Catalyst 3500 Problem

I've recentley upgraded a network in one of my locations.  It contains two Cisco Catalyst 3548 in one closet connected via GBIC loopback adpaters.  There is an identical setup on the first floor.  The two closets are connected with Cisco's GBIC Fibre adapter. I've set the switches up in a cluster format with one of the switches in the second floor closet acting as the command switch.

The problem that I'm having has hapened twice now in the past week. Segements of the network will drop off, when looking at the upstairs switches the GBIC loop back port connecting the Command switch and one of the member switches is falshing amber.  I simply pull the GBIC cards out and reset them and all works fine.  The first time I figured maybe it's just a fluke, but it's hapened again.  When looking at the diagnostic log this is what is a portion of what is shown...

I'm kind of new to the Cisco IOS and am just learning the CLI and have mostly been using the web bsed management. If anyone has any ideas I'd really appreciate it.  Thanks in advance.

Interface FastEthernet0/48, changed state to down
4d20h: %LINK-3-UPDOWN: Interface FastEthernet0/48, changed state to up
4d20h: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/48, changed state to up
4d20h: %LINK-3-UPDOWN: Interface FastEthernet0/48, changed state to down
4d20h: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/48, changed state to down
4d20h: %LINK-3-UPDOWN: Interface FastEthernet0/48, changed state to up
4d20h: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/48, changed state to up
4d20h: %LINK-3-UPDOWN: Interface FastEthernet0/48, changed state to down
4d20h: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/48, changed state to down
4d20h: %LINK-3-UPDOWN: Interface FastEthernet0/48, changed state to up
4d20h: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/48, changed state to up
4d20h: %LINK-3-UPDOWN: Interface GigabitEthernet0/2, changed state to up
4d20h: %LINK-3-UPDOWN: Interface GigabitEthernet0/2, changed state to down
4d20h: %LINK-3-UPDOWN: Interface GigabitEthernet0/2, changed state to up
4d20h: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/2, changed state to up
4d20h: %LINK-3-UPDOWN: Interface FastEthernet0/27, changed state to up
4d20h: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/27, changed state to up
4d20h: %LINK-3-UPDOWN: Interface FastEthernet0/27, changed state to down

Answer : Problem: Cisco Catalyst 3500 Problem

Sounds like either a bad cable or a bad GBIC...  Try swapping the second floor GBIC's with the first floor ones and see if the problem moves with you.  If not, you likely have a cable problem.

Also, look at your interface statiscs and see if you are getting lots of errors.  That is the first sign of layer one issues.  Let us know if you get the layer one stuff ruled out, and we can go from there.