cabling problem switches crash every day


At the beginning I will sorry for me English I^m originally polish. I will try me best to ask understandable question.

I have very complicated problem but I'm sure the answer is easy.

I bought switch netgear  GS748T  it  was working fine few month and then starts problems. Once per day it stop working yo I need to restart and like that every day. I put different netgear switch FS726T in his place and everything was working fine.
I send switch back and receive new one and he has similar problems so i send them back this switch and wait for another replacing switch. Network was working on  FS726T without any problem.

I bought another switch this time linksys SLM2048 I connect him and then on this switch some of the pc was working fine some doesn't  work at all. I use the same cable us for  FS726T i try to connect to different ports reset switch nothing help. Then I change cable and works fine on other cable.

So I thought is cable but I install second card on one of the pc and connect with the cable that first card was not working and second card works fine.

I tested 15 different cables and sometimes i didn't have connection at all icon with red cross on PC
sometimes i have limited connection that means i  can send but I don't receive. But the same cables connected to other switches in company works fine. I have simply LAN tester all cables looks fine some of them i did(I thought that must be reason) but some of them was bought in shop and still the same.

I live network like that and I receive again netgear  GS748T because of some mistake i receive two unit(I'm not complaining) I connect them to the linksys and I connect one PC on each for testing

and here is problem like that that is working fine one day and then on one of them i loose ping to him but i can ping pc that is connect to him but ping are very slow like 40 ms or more but pc is working fine.

On second netgear I connect works fine I can ping him PC on this switch also works fine so i decide to put PC from the first netgear with slow connection to the second switch but when i plug cable nothing happens limited connection after reset both of them everything back to normal.

On the first netgear when I unplug cable the light is still flashing on switch like the connection is still activeted.

ANY idea what is problem. I don't thing is switches because I use five different looks like cable but how can I test them.

My network:
2 DC win 2003 r2
1 exchange win 2003 r2
getaway win 2003 r2 ISA 2006
few file server and database in FOX
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hmmm, it is possible you have loop within your network.

please try to take your netgear switch and connect only two pcs to it. then try to ping one pc from another.
if everything is ok, then try to connect another pair of PCs...
possibly you will be able to identify looped wires.
If you are keeping the network very simple you can eliminate the possibility of a loop.
There is a big chance that the problem could be with a network card or driver. If the same pc was used every time the problem eas observed I would look at replacing the network card.
gowermanAuthor Commented:
This is not problem with one pc.

If I make loop on linksys then it stops imediatly  I check that before. On netgear for the moment is connected one PC on each and they are connected to linksys so there is no way of loop. I connected netgear to diffrent switch(not linksys) and also was the same problem.
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what kind of network cards do you have?
do you have cards in 10 mbps half mode?
gowermanAuthor Commented:
No I don't have 10 mbs

I have 1gb and 100mb and I use auto negotiation.

Usually I have card on motherboard. Realtek rtl 8168 and i updated driver but no change
and nvidia nforce networking controler

Realtek is not working with all cables

nvidia I didn't check becouse is working and that production environment so I can mess around

gowermanAuthor Commented:
I change card in on one of the PC for INTEL PRO. On this card there is cable test that you can make. I did that and one of the cables was without one par so it can be use for 1GB connection I replace cable make test again and passed all. I live like that and today the same all netgear switches go down  and then I nedd reset them.

I tested yesterday few cables Pc's and cards and what I discover that linksys switch is also down but I can ping it and all connection that it has are still ok but I can't add new connection
I didn't reset linksys beacouse is main switch and all the servers are connect to it.

netgear after dwon:
I can't ping switch
Pings to PC'S on that switch are slow  40-70 ms
you can't add new connection and when you unplug connection the lights are still flashing

linksys after down
I can ping switch
Pings to PC's on switch are ok  1ms
you can't add new connection

What can occur problem like that

I think that I have more bad cables that they are not working with 1gb  connection

Do you know good lan tester (not fluke- to expensive) that detect more than physical connection


please do the following
install wireshark on your PC (
and then capture some traffic when your network seems down. I want to understand what is happening there
please save that file in native pcap file, but prior to attaching it rename it to txt in order for EE to accept it.
It would be enough tho see some packets captured.
gowermanAuthor Commented:
I replaced cable during weekend and looks like  that was the problem since yesterday no problem with the network
Please continue to monitor your network for another couple of days.
And then come back with the results.
However it is very unclear for me, how such a problem can appear suddenly one day.... Wiring is rather permanent, so possibly someone has made changes to it...
This is very possible if there is a physical problem with a cable, or one of the cable's ends. Is everything still working?
how is your network feeling itself?
gowermanAuthor Commented:

Problem was not a cables but program "THE DUDE" that i use for monitoring network.

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Nice job on finding the issue. Software can often cause unpredictable issues, and one of the best troubleshooting techniques is to disable any related or unnessisary software when testing for these types of issues.
btw, known behavior of dude's snmp monitoring. I have seen the same problem with d-links
prefer using advanced host monitor instead.
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