Want to win a PS4? Go Premium and enter to win our High-Tech Treats giveaway. Enter to Win


Network segment dropping connectivity

Posted on 2013-05-28
Medium Priority
Last Modified: 2013-05-31
Good day, experts,

I seem to be having a bit of a quandary and I was wondering if any network cable / electrical gurus might be able to shed some light on the problem that I am having.

It seems that as of late there is one particular segment of our network which just stops working out of the blue. This has happened twice, now. Here are some of the details:

- This segment uses standard CAT5e UTP cable.
- This cable serves as an uplink between 2 HP switches - a 16-port JE005A (Foundry office) and an 8-port J9449A (QA Office).  I would guess that this segment is around 125 to 175 feet long.
- The run is in a fairly noisy environment (a foundry) - it currently crosses some electrical wiring and is in proximity by a few metres to a Thermfire sand reclamation machine, however activity of this machine does not seem to correlate with the failure of the network segment.
- All other connections on both switches still function normally.

When the failure first happened, the link lights went out on both switches. Moving the the cable to a different port on the switch at either end did not fix anything.  The cable's conectivity tested fine, but since I had ample slack at both ends, I re-crimped both ends - the problem remained.

I replaced BOTH switches with new respectively identical backup models.  The result was the same. The network uplink segment would not link up while everything else still seemed to work normally. (All devices on their respective switches could still talk to each other - the failure was strictly with the uplink segment.)  I put the original switches back.

For one fleeting moment the link appeared to come back but the interface on the switches indicated that the link was at 10Mb rather than its usual 1000Mb. If I tried to ping one switch from the other, the response time was all over the map, from several hundred milliseconds to timing out.  This lasted for a couple minutes and the segment link went dead again.

So I decided to experiment and swap out the 16-port in the foundry office with the new 8-port backup switch.  When I did this, it didn't work at first, but when I picked up the little 8-port switch in my hands, the link came on.  I set it back down, and the link went out again.  The thing to note here is that when I set it down, it was directly on top of the existing 16-port swtich - metal on metal. I put a foam mat in between the two switches, and the uplink worked again.  I could then uplink the this 'middle' switch to the 16-port and everything was back up and running like usual again, except I now have a third switch bridging the gap between the two originals.

A point of interest - a few days later I tried plugging the uplink back directly into the 16-port, and it worked fine again.  Whatever noise or interference (I'm assuming this is what it was) had settled down the the point where it was no longer a problem for awhile.  I am interested in hearing if anyone can tell from this description what the most likely cause of the problem was. I get the impression that there is some sort of grounding noise or issue of some sort at play here, but if anyone can shed some light I would appreciate the input.

I spoke to our electricians and unfortunately they do not seem to have equipment which can measure noise on the network cables here.  They suggested that running an outdoor-rated cable outside of the building might help - however, is this where the problem lies?  The thing that throws a wrench into the works for me is the fact that 'grounding' the one switch to the other by setting it on top of it caused the link to go down, but removing that ground restored the link to working condition.  I have no idea if that says anything meaningful about the source of the problem.
Question by:LostInThought
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
LVL 18

Assisted Solution

by:Andrej Pirman
Andrej Pirman earned 360 total points
ID: 39201419
Well, as per your description, there is a slight possibility it has to do something with randomness...too. But if you are pretty sure that grounding a switch renders link useless, then your problem lies most probably in mechanical failure of the uplink cable.
I doubt it being interference, or better, induction from surrounding machines, as it sounds like current is flowing through one of the cooper wires to the ground.

Uplink falling to 10Mbit is the indication that wires are cut or have bad conductivity. Might be induction, too, but I doubt. Rather it is insulation poor on some region, letting moist in, so your problems might also be weather-related.

My first bet would be: lay another CAT5 FTP twisted-pair cable, with metallic shield (be it metallic paper or wired shield)
LVL 22

Assisted Solution

by:David Atkin
David Atkin earned 360 total points
ID: 39201420

Installing an external grade cable won't make much difference I don't think, you would need a shielded cable not an external one. Ideally you need to get the cable tested to confirm if there is interference on it.  The cable may even be damaged if its in an active work area.

Would it be possible to re-route the cable or to install a new cable away from any of the power cables?

From what you have said, it does sound like either an electrical issue or a fault with the cable. Both can be tested by a qualified cable installer.

Assisted Solution

TunerML earned 360 total points
ID: 39201423
A lot of variables here, first thing I would try is replacing the Cat5e run between switches so distant with Cat 6 which is more resilient to interference and noise and handles distances a bit better.
Concerto Cloud for Software Providers & ISVs

Can Concerto Cloud Services help you focus on evolving your application offerings, while delivering the best cloud experience to your customers? From DevOps to revenue models and customer support, the answer is yes!

Learn how Concerto can help you.


Accepted Solution

BigPapaGotti earned 420 total points
ID: 39201424
Were both of these switches 100MB or 1000MB? I've came across a similar issue before where the switches were gigabit but the link would go up and down constantly due to the length and noise on the cable. Finally hardcoding both switches to 100MB Full Duplex allowed the link to stay up without any intermittent drops.

I know this does address the electrical side of things but I just wanted to be sure I understood the problem fully. Also as you mentioned the cable that is running between these two switches is going over some electrical wiring which is not recommended and could be causing the problems you are having. The switches may just be handling the problem a bit differently.

Author Comment

ID: 39201600
Thank you for the responses.  The general consensus seems to be that the existing cable is the problem and that running another cable away from the electrical interference would be advised.  This is probably the cheapest option for us at the moment - we don't really have anyone available who can do a proper test on the existing cable for noise/interference.

As far as shielded cabling goes, my initial bit of research seems to indicate that we would require not just that one segment to be shielded in order for it to be effective, but all the equipment would also need to be properly grounded as well, and given our current layout, that could be a bit problematic - this is a very old building which I am sure also needs electrical improvements, but this is the first real problem we've run across.

It is possible to run another cable, but the only realistic way for us to keep it away from electrical wiring would be to run it outside the building.

I had not thought of manually setting the speed to 100Mb on both switches -  I will keep that in mind as a possible option. For now I will put in a service request to have the electricians run another cable outside the building.  It is just that from what I have read, I have my doubts whether using STP cabling just for that segment alone will help.
LVL 17

Expert Comment

ID: 39202092
Perhaps running a fiber-link could be an idea.
Fibers will not pick up noise.
Fibers isolate.

Author Closing Comment

ID: 39212217
We will be running another cable away from the electrical wiring, so I am awarding points to those that suggested re-running wire, but also giving points to BigPapaGotti because the manual setting of the switches to 100Mb seems to have really helped in the interim - I feel silly for not having first tried it myself.  Oh well, that's what the experts are for!

Featured Post

Understanding Web Applications

Without even knowing it, most of us are using web applications on a daily basis. Gmail and Yahoo email, Twitter, Facebook, and eBay are used by most of us daily—and they are web applications. We often confuse these web applications tools for websites.  So, what is the difference?

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

This article will inform Clients about common and important expectations from the freelancers (Experts) who are looking at your Gig.
WARNING:   If you follow the instructions here, you will wipe out your VTP and VLAN configurations.  Make sure you have backed up your switch!!! I recently had some issues with a few low-end Cisco routers (RV325) and I opened a case with Cisco TA…
If you're a developer or IT admin, you’re probably tasked with managing multiple websites, servers, applications, and levels of security on a daily basis. While this can be extremely time consuming, it can also be frustrating when systems aren't wor…
NetCrunch network monitor is a highly extensive platform for network monitoring and alert generation. In this video you'll see a live demo of NetCrunch with most notable features explained in a walk-through manner. You'll also get to know the philos…
Suggested Courses

636 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question