UDLD to stop Bridging Loops

[mgerron]

We are an all Cisco shop with 3500XL at the edge with a 4006 in the MDF at our remote locations. Every once and awhile we lose a site because of a $30 hub or switch that has an auto uplink port in it plugged into a 3500XL. In some cases a user has plugged a cat5 cable from the hub back into the hub causing a loop and taking down the site or the auto uplink port malfunctions causing a loop until the hub has been powered off and back on again. Will UDLD help solve this? We are running portfast on all of our switches and would like to continue to do so if possible. Any ideas?

[dgahm]

What you are describing can be best prevented with the use of BPDU Guard. When used on ports that have portfast enabled it will immediately shut down the port if BPDU frames are seen. This would happen if a user loops the port. You should not use it, or portfast, on ports that connect to network devices.

This command was introduced with version 12.0(5)WC5 for the 3548.

The interface command would be:

spanning-tree portfast bpduguard

On the 4006

set spantree bpdu-guard X/X

http://www.cisco.com/en/US/tech/tk389/tk621/technologies_tech_note09186a008009482f.shtml