APLawrence.com -  Resources for Unix and Linux Systems, Bloggers and the self-employed

Switches damaged by UPS?

Wed Oct 6 12:38:29 2004 Switches Search Keys: hardware|problems

Yesterday I had an emergency call from a customer whose network was down. As I was familiar with the physical setup (old equipment, badly made cat-5 cables), I suspected cable failure at first, and yes, when I arrived on site and started testing, there were some cables that wouldn't pass a "wiggle test" - in other words, they probably worked most of the time, but if you put a little wiggle on the connector, they were apt to fail.

However, that wasn't the real problem. One of the users gave me my first clue when he said that around 3:00 PM he had been copying files from one server to another. He heard a longish "beep" and everything stopped. A long beep makes me think UPS, and that makes me suspicious of power surges, which makes me start thinking about blown switches.

Other evidence supported this: a very few people were still able to connect to some servers, though intermittently: one minute they'd check mail and Outlook would complain that it couldn't reach the server, a few minutes later a bunch of mail would come through. The same flaky access was seen for Internet access.

Testing is not too difficult. First, I used a cross-over cable to connect two machines together. I chose two Linux boxes, and verified that they could ping each other and transmit some files without error. The purpose of this was to be sure no damage had been done to their NIC cards. Next, I took everything off the nearest switch and plugged these two servers into that. Moving wires from port to port, I quickly found that most of the ports were dead or very close to it. The only good ports were those that had not had any wires plugged into them.

That switch was not directly connected to the UPS, but it was daisy chained to another switch that was. Like so many places, these folks had outgrown their switch capacity and had daisy chained rather than buying larger units. Physically, a 24 port switch in another part of the building fed an 8 port (which was the one plugged into the UPS), which then went to the 5 port that I first tested, and to another one in the next office. I repeated my test with the 8 port and found that several ports there were dead or weak.

It was obvious now that we'd need some hardware. We sent someone out and they soon returned with a 16 port and a 5 port 10/100 switch. At this point I didn't know if the damage might extend to the 24 port across the building, but we couldn't buy that off the shelf anyway and I knew I could get at least part of the building running with the new switches. There were actually two 24 ports chained together, but they were too far away for me to conveniently test, so I just installed the new equipment and crossed my fingers. I still needed the 5 port just because of physical location, but we did eliminate one extra 5 port switch.

Fortunately, everything came up. Well, almost. One machine in a remote location wasn't seeing the network. I took a quick look and tried finding where its wire went to but lost it under heavy desks and file cabinets. It was getting late, people were leaving to go home, so we decided to track that one down the next day - it apparently wasn't a critical machine anyway. It could be a weak port, bad wiring, who knows? The customer will find it.

My suspicion is that the cheap UPS blew ports on two switches. I've seen UPS do things like that, and recommended that it be replaced ASAP. We also talked about network surge protectors, though I'm not sure those would have stopped this.



Got something to add? Send me email.





(OLDER)    <- More Stuff -> (NEWER)    (NEWEST)   

Printer Friendly Version

-> -> Switches damaged by UPS?




Increase ad revenue 50-250% with Ezoic


More Articles by

Find me on Google+

© Tony Lawrence



"My suspicion is that the cheap UPS blew ports on two switches. I've seen UPS do things like that, and recommended that it be replaced ASAP."

There's no such thing as a good, cheap UPS (or a good, cheap anything in the world of computers). BTW, who made this "cheap UPS?"

"We also talked about network surge protectors, though I'm not sure those would have stopped this."

My experience has shown that network surge supressors are usually a waste of money. If all hubs/switches/routers are powered by a quality UPS then there's no reason for abnormal voltages to ever appear on the network lines -- unless network hardware in building A is connected to network hardware in building B. In such a case, the physical link should be something other than copper -- fiber-optic or wireless for those who are feeling lucky. With copper, ground plane potential imbalance (GPPI) could make the link unstable.

Speaking of network surge supressors, there's some evidence to suggest that they can degrade the signal quality, causing UTP Ethernet links that are close to the 100 meter limit to become unstable.

--BigDumbDinosaur

---October 6, 2004

I was taught that when connecting buildings, or multiple floors in a same building you run into problems with grounding. Even though each building/floor is grounded, there is a voltage potential difference between the 2 buildings, and if you only have a network card connecting them, then the buildings will try to equalize THRU the networking cable... Which is bad.

Maybe the building's electrical system isn't well grounded. Or all those bad UPS/daisy chaining them will cause similar problems...

But then again it makes sense that if piece of computer hardware is failing it's not unlikely that similar hardware built at the same time period on the same assembly line would be about ready to die at the same time.

(BigDumbDinosaur does know what he is talking about, BTW)

--Drag

---October 6, 2004

"(BigDumbDinosaur does know what he is talking about, BTW)"

You won't get any argument from me :-)

--TonyLawrence

Now that's what I call affirmation! Give me enough of that and five bucks, and I can go to MacDonald's and eat in style. &lt;Grin&gt;

"Even though each building/floor is grounded, there is a voltage potential difference between the 2 buidlings, and if you only have a network card connecting them, then the buildings will try to equalize THRU the networking cable... Which is bad."

In other words, GPPI. It will also screw up EIA-232 serial links big time.

--BigDumbDinosaur

Kerio Samepage


Have you tried Searching this site?

Unix/Linux/Mac OS X support by phone, email or on-site: Support Rates

This is a Unix/Linux resource website. It contains technical articles about Unix, Linux and general computing related subjects, opinion, news, help files, how-to's, tutorials and more.

Contact us





The worst crime against working people is a company which fails to operate at a profit. (Samuel Gompers)

er.












This post tagged: