FastEthernet is up, line protocol is down

Posted on 2005-04-15
Medium Priority
Last Modified: 2013-11-29
Hi there.

I have a Cisco router (IOS12.1) with two FastEthernet interfaces (as well as BRI and Serial) one of which I can no longer connect with.

I did a "show int fastethernet" and it is showing FastEthernet is up but line protocol is down.  It looks like it's been down over a week (from last input/output stats).

What could this be an indication of?  An unplugged cable, bad interface...?  Should I do a shutdown, no shutdown to try to bring it back up?  Could I loose the config doing that?

I don't have local access to the router at present.

As always, any help is greatly appreciated.

Question by:ttist25
LVL 27

Accepted Solution

pseudocyber earned 2000 total points
ID: 13791708
>>What could this be an indication of?  An unplugged cable, bad interface...?   Yes, it could be any of those - a cabling problem.  Layer 1 problem.

>> Should I do a shutdown, no shutdown to try to bring it back up?  You can try that.

>> Could I loose the config doing that? No, but just to be sure, why not do a copy run start first thing you have access to them, unless your policy is to maintin different configs (I've heard of that before).  Or you could tftp the running config to a laptop or something.

Definitely check the physical cabling.  You might need to take some cable testing equipment with you - like a Time Domain Reflectometer (TDR) if you have on, a wire mapper, or at least some kind of continuity tester if it was a previously working cable.

Author Comment

ID: 13791835
I'm in a limited, contract, support capacity and am not intimately familiar with the setup so am trying to tread lightly.

I'll try the shutdown / no shutdown and see if it helps.  I also remember seeing reference to an interface  rest command.  Is this something I should also try?  Can you provide the syntax?

Thanks for the quick response.
LVL 32

Expert Comment

ID: 13793757
It also could be a problem on the switch, bad port etc .......  What type of device doe sthis interface connect to?
Have you looked at the port stats from that device's perspective? errors, config changes, etc .......


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