2950 Switch - Port Confused (This was a strange one!)

Unanswered Question
Sep 4th, 2009

I've now seen the strangest thing ever on one of our switches. Earlier today we had a section of one of our schools lose wired and wireless connectivity. I checked and saw that one of our switches had stopped responding and appeared offline.

Logging into a neighboring switch the trunk port (gi0/2) was showing up/up. Ok wierd. So I went out to the site and consoled into the 'down' switch. It's trunk port (also Gi0/2) was also showing up/up. I unplugged the cable from gi0/2 and my console showed Fa0/24 going down/down. Huh? I plugged it back into Gi0/2 and console reported Fa0/24 going up/up.

Totally baffled now, I configured the empty Gi0/1 as a trunk and connect the cable to that port instead. The console showed Fa0/24 go down/down and then Fa0/17 come up/up! Yet still no connectivity/visibility to the next upstream switch.

I reloaded the switch from the console, not saving any changes I had made, and it came back up - now connected and able to see the next switch.

Is this a sign of the switch giving up the ghost? Has anyone experienced a switch getting it's own ports confused like this?

Even if I can't really 'fix' it, it's one of the funniest things I've ever seen a Cisco switch do. :)

I have this problem too.
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simontibbitts Fri, 09/04/2009 - 23:32


The link state tracking feature will create this behavior where downstream ports will change their state depending on upstream ports. Check the configuration to see if it has been configured.

Otherwise, I agree. Strange one!


Leo Laohoo Sun, 09/06/2009 - 14:32

Firstly, is the uplink ports copper or fibre? If it is fibre, did you enable udld port aggressive?

Secondly, depending on the IOS running, how long do you think was your switch been up since?

glen.grant Tue, 09/08/2009 - 08:15

Sounds like you have some physical loop somewhere , this can easily take down the whole switch . It's possible when you reloaded that spanning tree was able to resolve that loop and put the ports into a blocking state. Try a "show spanning tree blockedports" command and see if there are any ports in a blocked state.


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