Strange Netwoking Problem, Need Expert Advice

[huntc919o]

When the problem stumps the rest, talk to the best... which is why I'm here hoping someone can shed some light on this problem.

First of all this problem appears to be a physical layer problem and isn't specifcally related to Cisco hardware.

I have a networking problem between two buildings which are approximately 75 feet apart. At present, the 2 buildings are networked together with a single switch in both buildings, connected together by a CAT 5 Xover cable. The cable itself is a normal UTP cable which is suspended in the air between the buildings. (Scheduled to be replaced with an underground fiber connection in the spring).

The problem that has begun to occur is that connectivity between the 2 buildings is being lost which only seems to occur whenever there is a bad snow storm. The CAT5 cable tests out good under these conditions.

In both buildings, the CAT5 cable enters the building approximately 5 inches from the floor then runs up the wall, along the ceiling, then down to its destination.

The problem has been isolated to the ports blowing out in the switches located in bldg A & B. When the Xover cable is moved to a new port on each end, connectivity is restored....that is until the next snow storm.

This has only happened twice, but I would like to determine the cause of the problem before I replace both switches.

I would really appreciate it if someone could give me a few ideas as to why the ports on the switches are starting to blow out.

Thanks in advance,

Cliff

[Kevin Dorrell]

When this happens, and you move the cable back to the original port, does it work again? That is, is it a lockup, or is the port destroyed? Does it work again once you reboot the switch?

The two ports that failed - were they on the same switch or on different sides of the cable?

The snowstorm seems to suggest something. My guess would be lightning strike, or something massively inductive. Do you have any electrically heated (de-iced) road under the cable?

The only other thing I can suggest is aurora - since you are talking of snowstorms, are you in Canada or somewhere very north? I have heard that northern lights can disrupt power distribution in Canada. However, that does not really fit because we are aproaching the sunspot minimum at the moment. (The minimum is actually around 2007, and the cycle is 22 years).

Kevin Dorrell

Luxembourg

[huntc919o]

When the problem occurs, rebooting the switch has no effect.

The ports on both sides of the cable are destroyed.

There isn't an electrically heated road under the cable.

I'm located just outside of Pittsburgh, PA.

Cliff

[Kevin Dorrell]

The electrically heated road was just a wild shot : I heard they have heated driveway ramps in some parts of Sweden for example.

It sounds most like a lightning strike. Probably not a direct hit, otherwise you would see a lot more damage, but a hit on a nearby lightning conductor maybe. (Never twice in the same spot?) Was there any thunder in the area at the time?

Kevin Dorrell

Luxembourg

[glen.grant]

My guess would be some where in the cable you have a minute hole in the sheath of the cable where water gets in and shorts a couple of the leads together and when it drys out it is ok . If you have the option I would replace the cable if it's only 75 feet .

[Kevin Dorrell]

Cliff,

I had another thought about this. Do the two buildings share a common electrical ground ... apart from Mother Earth, that is? If not, and there is any imperfect grounding in either building, then they could be trying to find a path to earth through your cross-cable. But if that were the case, I would expect to see a greater-than-normal number of CRC errors on the line as well. Why it should be particularly so in a snow storm, I don't know ... emergency generators switching on, extra heating, etc. In any case, that would be resolved by moving to optical.

If you want to verify the grounding, you had better call an expert. I could not advise you, and I am sure that standards are different over your side of the pond.

Kevin Dorrell

Luxembourg

[jroyster]

I'm with Kevin on this one. As soon as I read "cat 5 between buildings" I immediately though "ground potential"

then when you said the ports were getting damaged that pretty much nailed it.

I believe there are grounding/protection kits for CAT5 and they may even be required by electrical code. I'd suggest having a professional cable installer take a look.

[alex.walker]

Agreed. You need electrical isolation.

The BBC in London is a classic example. The ground potential differs by 2v at opposite ends of the building!

An isolating transformer on the AC input might help, or use a UTP -> Fibre -> UTP conversion at one end?

[huntc919o]

Thanks to everyone in helping me out with this problem. I know one of the 2 building is properly grounded but I'm not positive of the second building.

The difference in ground potential was in the back of my mind but I wasn't positive since I've never run into this type of issue before.

As a temporary solution I'm going to put a cheap Linksys switch on both ends of the cable to keep from blowing out more ports in the existing switches.

Hopefully, this will allow me to keep things running until the fiber and new switches can be installed.

[huntc919o]

I also found some RJ45 surge protectors to help reduce the problem.

[alex.walker]

Don't know if they'll help. They're designed to help with mains spikes or lightening hits etc.

I would try getting a cheap pair of UTP to Fibre converters, and patching them together with a short fibre patch cord. This will electrically isolate your UTP.

[b.orth]

Interesting problem. But isn't a UTP cable designed for indoor use? A 75 foot span swinging in the breeze would make a substantial antenna, and probably capable of picking up an induced current from even a large cloud going by, like during a snow storm (even with no lightning).

All of my data circuits (no ethernet ports) that leave my building are protected by CSU's designed to deal with induced currents outside the building. To my knowledge nothing like this was ever done with an ethernet port.

But then again maybe the bits are getting frozen, and moving to a new port will heat them up again. ;)

Generally to connect two buildings, no matter how far apart, you need a Communications circuit designed to Isolate the different grounds, and dissipate any induced current.

HTH

[bvanderwoude]

I am with B.Orth here. If the cable is not rated for outdoor duty, then I am certain you will get a voltage differential between the two buildings that could destroy the chip sets in either or both switches. I think that if you could convince the "powers that be" that this is going to cost a far amount of money in equipment replacement unless the fiber is run earlier than later, you might be able to save youself some headaches. If a windy snowstorm will take these ports out, then just think what a thnderstorm will do!

Fiber is the way to go. March should be a reasonable time to get someone to work outdoors in PA.