Troubleshooting intermittent network outages on a Catalyst 3548XL.

[scottmilner]

Hello,

I have a client with four Catalyst 3548XL switches (containing 4 VLANS) that are experiencing sporadic network outages. During the failure, users lose connection to the network drives on the servers, printing fails, and the internet cannot be accessed. The failures affect all vlans, and the network seems to restore itself after 10-15 minutes.

The failures could potentially be isolated to the switch containing the servers, as printing, drive shares, and DNS requests all go through that switch... however, I am not seeing anything in the event logs of the servers to indicate a problem here.

The switches are all running IOS 12.0(5)XU. The show diagnosticlog shows me that many (not all) of the ports are changing states from up to down and back again. The show diag link-flap shows me that some ports are experiencing a large amount of link-flap errors (relative to other ports, but i don't know if 497 is an excessive number), but again, I can't isolate to a root cause from here.

Can anyone give me some troubleshooting tips here? As you can probably tell, I am a cisco newbie. Are there othere diagnostic logs available to me on the switches that I am unaware of? I will attach one of the configs.

thanks,

scott

[cowetacoit]

The root bridge just controls the STP on your network. Did you disable portfast default?

[scottmilner]

I haven't made any changes yet...I think portfast is still enabled on all active ports. I am taking notes on everything you and dominic are suggesting.

School is still in session, so I will need to implement changes after hours. We have had enough issues in the last couple of weeks that even a minor outage will ruffle a lot of feathers.