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Discussion Starter · #1 ·
I have a LAN consisting of 6 Cisco WS-C3550 48 port switches, and about 4 of the same 24 port switches.

My problem is, one certain switch keeps loosing its fiber link with another switch in a different closet. If you re-boot the switches, they will connect for a short while, but then loose the link again. This affects the whole LAN and the internet is not broadcasting like it should, because of the broken fiber link. What would cause a switch to do such? I've checked the network for machines with conflicting IP's, and so far haven't come up with anything.

Hyperterminal shows good, no error messages from either switch.

I'm LOST!!!!!

Does anyone have even a remote clue as to what the heck's going on???
 

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Yeah, the fiber is probably bad. Swap it out with a new cable.
If that is a problematic thing to try, put a different, known good switch in that closet. If the problem completely disappears, you've got some bad hardware on the original switch. But I'd put my money on having a bad fiber cable first.

-Scott
 

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Discussion Starter · #3 ·
I finally got an error message on the switch. It stated, ETHCNTR-3-LOOP_BACK_DETECTED

I can't seem to get the port back up now. Plus, what does this message mean?
 

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A port that detects a loopback is one that notices every packet it sends out, comes right back in on that same port. So, it is a physical "loop" back to the same port. It is trivial to create a copper loopback plug, but you'd need the right equipment to create your own fiber loopback plug, but it's still very easy to create. The same strand goes directly from the transmit to the receive side of the same fiber connection.

So, what does this error message mean for your problem? I'm doubting that you've intentionally created a loopback situation; It's very improbable that the fiber is damaged in such away to accidentally create an actual loopback. Since we're dealing with the same brand of equipment on both sides, it's possible one strand of fiber is bad, but the other is OK, and it just so happens the physical "hello" traffic the two switches sent out was closely enough synchronized that one of the switches incorrectly thought there was a loopback. It's also possible a hardware problem on one switch causes the traffic from the other to be simply piped back out the same port. It may also be possible to configure the port that way...

So far, you've not helped narrow the problem down at all, and I'm still going to insist that you swap out or otherwise test to ensure the fiber to that closet is in good shape. Until that is done, I can only continue to guess at possibilities.

-Scott
 

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Discussion Starter · #5 ·
Well, I found the problem. I had a Microsoft wireless router hooked into my lan for my laptop's wireless card. It was somehoe creating chaos on the wired side of the network. All I did is remove this piece of hardware and so far everything is fine!
 
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