I have two 6509 switches running Sup2 and CatOS with virtually the same configuration. Until recently they were connected to a 2950 (trunking 3 vlans) at 100mbs using media converters on both ends of a fiber run.
To get rid of the converters and increase bandwidth, we purchased a 2960G-24TC-L to replace the 2950 and ws-g5484 gbics for the 6509's and glc-sx-mm sfp for the 2960.
One switch works fine.
The other switch will pass traffic for about 10 minutes, and then the connection will go down for about one minute before coming back up. This repeats with regularity.
I re-installed the media converters and connected the affected switch to the 2960 and it works fine.
My initial thought was that I have a bad gbic/sfp but I swapped out the actual gbic/sfp and used a different slot but the problem persisted.
Because the connection would go down for about a minute I considered some spanning tree problem, but then I would have expected it on both switch connections.
I have been looking at the counters on the CatOs and the Controller output of the IOS and the only peculiarity is on the affected switch there were quite a few rxoversized packets/ifInErrors/dot3statsFrameTooLarge.
Would that be evidence of a bogus gbic? Any other ideas on troubleshooting?