[27216] in resnet
Re: Ethernet ports "burning out"
daemon@ATHENA.MIT.EDU (Isaac Holmes)
Thu Jan 26 23:36:30 2012
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Date: Thu, 26 Jan 2012 23:36:21 -0500
Reply-To: Resnet Forum <RESNET-L@listserv.nd.edu>
From: Isaac Holmes <iholmes@ND.EDU>
To: RESNET-L@listserv.nd.edu
In-Reply-To: <4F2223E6.7000102@tcnj.edu>
Your mentioning the location of the jack near the bed reminded me of an incident we had a number of years ago with in a dorm room. Being that the jack is on one side of the room and the students always seem to want the computers on the other side of the room they have 30-50 foot cables strung around the room.
This particular room the jack failed repeatedly over move in week. When we went to the room to investigate we found the 30' cable strung around the floor of the room and when I was pulling it up to inspect it I found the cable had ended up under the leg of the metal bed frame. As it turned out there was also a short extension cord right next to it. As I went to move it the leg of the bed cut through both the network cable and the extension cord. Nothing like popping a circuit breaker and turning off power to half the floor of the dorm.
After replacing his cable and making sure it no longer was being cut by the bed we had no more issues with that room.
Isaac Holmes
Client Engineering Specialist
OIT Distributed Engineering Support
University of Notre Dame
B036 IT Center
(574) 631-3254
-----Original Message-----
From: Resnet Forum [mailto:RESNET-L@LISTSERV.ND.EDU] On Behalf Of Brad Coburn
Sent: Thursday, January 26, 2012 11:11 PM
To: RESNET-L@LISTSERV.ND.EDU
Subject: Re: Ethernet ports "burning out"
Thank you all for your ideas, comments and support.
Facilities replaced the cable this afternoon, tech re-terminated everything and confirmed data is flowing, so now we wait.
If the problem recurs, we will separate the connections between two closet switches. Not that I want dead ports on two switches, but maybe the isolation will be sufficient to show us something.
Next after that will probably be to patch them back into the desktop Netgear in the closet. I prefer to keep any equipment locked up and out of the hands of the students.
The switches are Extreme Networks, Summit 200-48 (old) and Summit X250e-48t (the new one just installed).
Let me toss this out there: What does anyone think about (severe) ESD
being a possibility? It's winter time, humidity is low. The bed is right
next to the jack. Maybe a large charge developed between PJs and bed
covers? Like most of us, I get some nasty shocks this time of year. I
think it's a stretch, but if you're writing a paper while lounging on
the bed, no power supply connected, and happen to get up or sit down and
touch that patch cord, or even just the machine, perhaps the UTP
connection is a good enough drain for a large static build-up? Or
another way to ask this, is why would this NOT be a serious
consideration? (Besides about 3500 students in residence who haven't
have this problem on a regular basis over almost 20 years?) LOL
In the meantime, to some of the suggestions and comments:
* Did the ports recover after they were unused for a while, or
were they blown? (and similar thoughts about enabling/disabling ports)
--The Extreme SE recommended toggling the port enable. No change. I even
tried looking in the log to see if maybe the switch detected station
link up but wasn't able to respond. No dice. The switches that have had
port problems in the past don't experience "reanimation" (unless someone
mis-diagnosed the problem and incorrectly tagged the port bad). Very old
models cascade failure to 4- and 8-port groups when the ASICS finally
go. Our experience with port failures on switches in other buildings
(since we didn't always believe that a port could really "fail") is that
they're toast.
* To the vendor/TAC calls, it's something on the to-do. We have an email
for our SE and he had some off-the-cuff suggestions but nothing
groundbreaking. We have RMA'd switches with bad ports back, but all they
do is ship a replacement unit and close the call. We will try to see if
we can get someone to actually work the problem when things calm down.
* Where did you check pair to ground voltage? In the closet or
in the room? It sounds as if you have a floating ground in the room,
but if you checked voltage there, maybe not.
--Tried to check that. I have a 3M tester used for telco OSP copper
testing. Looked at tip-ring and tip/ring-ground for each pair, both
voltage and resistance. Used the TDR function, alone and comparative
(two pairs simultaneous); nothing apparent. The equipment rooms are
powered with normal dedicated circuits, maybe two; for these events no
other switches in the rack are affected.
* Can you isolate the PC and Mac on separate electrical circuits
to see which one fails again?
-- Didn't try this one, but it might be impractical. I believe the
building to be old enough that there's one 20A circuit per room. If not,
I'm not sure how to sufficiently and clearly explain the idea to them.
They do have their beds/desks on opposite sides of the room, so that
might achieve the goal.... Additional discussion around the office on
the topic of power-supply problems degrade into resignation that if
power was the problem something worse should be happening that would be
evident to the students.
* Is it an option to put an in-line circuit breaker on the port
connections?
--Definitely an option. I might have something in a back room somewhere,
otherwise I have a price for a device that might work. I only wish the
things would present an obvious fault condition; most of the devices
look like they will only fail obviously for a catastrophic event (e.g.
lightning).
* Is there a microwave, hair drier, or some other device that
may induce transients on the line? Maybe one of them has a bad power
supply.
-- Quite possible; the room is tight. However the typical room layouts
that student choose put all the appliances near the jack anyway; the
CATV port is there and the refridge/micro tower makes a nice TV stand
(if not terribly sturdy).
* Various comments about cable running past high voltage equipment or
facilities
-- There's nothing like that in the hallway ceiling or in the riser
rooms. We traced the cable through the ceiling. Hoped to find damage
where the bundles ended up against pipe hangers, but no dice.
-Brad
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