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Switch issues

Posted on 2014-07-28
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Last Modified: 2014-07-28
Experts! I would appreciate your feedback if any of you have run into this issue or have some clue as to what else I should be troubleshooting.

The scenario is that on Friday, I connected two wall jacks to one of our network switches, and about the same time, a user reported that they lost all connectivity.

After troubleshooting, I found that the line going from our network switch to a small switch at the user's desk had connectivity, but when you plug it into her switch, there's no connectivity. It doesn't assign any IP, and if you set the IP manually, it still has no connectivity. I swapped the smaller switch, but surprisingly, ran into the same issue.

I might understand if there were an issue with the network switch that was somehow caused by connecting the two jacks that I did (although I tried disconnecting them again, which had no affect), but the fact that the line coming into the smaller switch works just fine if you connect it directly to a computer is puzzling me.

To add another level of mystery, if I connect the same smaller switch to a different line coming in from the larger network switch, everything works as expected. So this one has me a bit stumped.

Am I missing something obvious? Any constructive feedback you may have to offer would be appreciated.
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Question by:rpmccly
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by:Joshua Grantom
Joshua Grantom earned 166 total points
ID: 40224469
Do you have a cable tester that will provide you the length of the cable run from the large network switch to the smaller switch?

Max run length is 328 feet. This could be causing communication issues
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by:tolinrome
ID: 40224482
" I connected two wall jacks to one of our network switches, and about the same time, a user reported that they lost all connectivity." - You connected two cables from the wall jacks to the switch? What were those ports connected to on the other end? If a switch how are the ports configured?

One problem at least lies between the smaller switch at the users desk and the main one youre mentioning. You need to make sure its a crossover cable between these two switches. Also, how is this small switch configured?
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by:rpmccly
ID: 40224488
I'm glad you mentioned that because another twist I forgot to mention is that I inherited this cabling, and this particular drop isn't labeled at all, so I don't even know which port on the network switch that it's connected to. Awesome, right? So while I do have a cable tester, I wouldn't know which cable to test!

That aside, she's been using this same drop for years, so I can't imagine cable length all of a sudden becoming an issue, and even if it somehow were, this particular cable run is probably closer to about 100 feet or less.
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by:Joshua Grantom
ID: 40224494
What kind of switches are they?
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by:pony10us
pony10us earned 167 total points
ID: 40224513
To determine which port you are plugged into there is the old fashioned way:

1. check what ports have connectivity (light)
2. disconnect device
3. check what port now doesn't have connectivity (light)

or depending on what tester you have:

1. disconnect device
2. connect tester and select the option to flash the switch port
3. look at the switch for the one that is flashing consistently
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by:rpmccly
ID: 40224536
@tolinrome: I'm sorry, I should clarify that the jacks didn't have any equipment connected to them at the time. All I was doing was connecting the jacks to the switch so that they'd have connectivity. So essentially, I was just connecting a cable that wasn't connected to anything yet. It's seemingly insignificant, but the timing seemed too coincidental not to mention. Plus, even if I disconnect those jacks, the issue persists.

Regarding the smaller switch, I'm not sure why it'd need a crossover cable, especially given that the drop it's been using has been functioning for years. Would you mind elaborating on that one?

The smaller switch is a TrendNet TE100-S80g, which is just a dumb switch. So to my knowledge, there isn't really any configuration.
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by:pony10us
ID: 40224580
"auto-uplinks to any other switches on the network, no crossover cables needed"
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tolinrome earned 167 total points
ID: 40224581
Ok, thanks for clarifying. Maybe I understood wrongly, but I assumed the network switch is connected to the smaller switch, which the user is connected to? If that is the case I was just saying that the cable between the two switches should be a crossover cable (at least thats they way I was taught).

Anyway, since you connected the smaller switch to another switch and tested connectivity fine and when you connect it back to the original one and it doesnt work could it be a cable issue. On the network switch if you plug directly into it does it give connectivity?
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by:rpmccly
ID: 40224612
@Joshua G: The larger switch is either a Linksys SGE2010P or a Cisco SG200-50P, and the smaller switch is a TrendNet TE100-S80g dumb switch.

@pony10us: Yeah, I might have some manual labor ahead of me since that would involve testing about 75 ports, and I'd be disconnecting random users in the process if I did it during normal business hours. That aside though, wouldn't I be looking for ports that don't have connectivity on them, given that connectivity is the issue? If I only test jacks that don't have any connectivity on them, that'd whittle things down significantly and shouldn't interrupt any user connectivity.

I should mention that on the smaller dumb switch, when I plug the cable in that comes from the larger switch, the '100MBps' light would flash once or twice and the 'LINK/ACT' light would flash maybe once and then go dark. So the only traffic I see on the side of the dumb switch are from the devices connected to it (but not from switch to switch).

@ALL: Get this, it randomly started working again. Now I'm really puzzled. I've checked connections repeatedly throughout this process to see if maybe there was a faulty cable or a loose connection of some sort, but I've never seen any change in connectivity. Now that it's working, I can't even duplicate the issue though - wiggling the cable, using a different port, or power-cycling the smaller switch. So being that I never understood the source of the issue to begin with, I have no guarantee that the issue won't resurface. So at this point, the only solid plan I have is to test until I find which port she's connected to on the network switch(es) and see if there are any apparent issues with that particular port. Any other advice?
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by:rpmccly
ID: 40224621
@tolinrome: It may well just be a cable issue that I'm just not able to replicate, but even when I was having issues with it, it worked just fine if I plugged it directly into a computer, which would seem to rule that out, wouldn't it?
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by:rpmccly
ID: 40224649
Scratch that, I was able to momentarily duplicate the issue when I was moving the cable around, so it's looking as though it was just a faulty cable. Thank you all for your helpful input in troubleshooting this though.
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