I am new as a Cisco admin and a recent CCNA. I have a perplexing problem. Recently we experienced a power loss in our switch core which consists of Catalyst 3550 switches. All links came up after power was restored except for two. One was a link to a Catalyst 2950 access switch and one was to a Catalyst 2900 access switch. Neither of these links came up. There is no link light and the status shows down, down (notconnect). I have checked the interfaces for any errors and there are none. The wiring is the same and has not been tampered with. There has been no damage to the wiring. The only change was a power loss to our switch core. Afterward the links to these 2 switches are down, down and will not come up.
Here is the really baffling part. I grabbed a HP Procurve switch and plugged the 2950 end of the link into it. I then plugged a patch cable into both the Procurve and the 2950. Viola! I got a link light on the 2950 and everything is velvet. I reversed the process and plugged the cable directly into the 2950 as it was originally and the results were the same as before. No link light; down, down(notconnect). I can only get the 2950 to connect if it is not plugged directly into the 3550 and instead is passed through the HP switch first. I have done all I know to do to troubleshoot this problem and am at a loss. From my training, the only reason I know of that a link could be down, down (notconnect) is if there is a layer 1 problem. Cable broken or damaged, simply not plugged in, a miss-wire...however, none of these are the issue.
Could someone please help this newbie out?
Very best regards.