Gaining & Losing Connectivity on LAN

I have a problem! On my LAN at work we have abour 40 XP Pro PCs, a Windows 2003 Server, a Windows 2000 Server, and a Sco UNIX Server. All of this is connected by three NETGEAR hubs, a Linksys BEFSX41 router, and a Linksys WAP54G Wireless Access Point for a couple laptops. A T1 provides internet connectivity. We also will have up to 6 VPNs accessing the network for Sales employees who are at their homes. The issue is that periodically (which can be 20 minutes or a few hours), all of the client PCs show on their desktop that they are losing connectivity and then gaining connectivity, back and forth. In the system tray of all client PCs is the tray icon for their NIC cards, which a balloon pops up and shows "Local Area Connection is Connected" then a red X over the icon. This flashes back and forth about every second. The only way I have been able to solve this is by shutting down all PCs and networking equipment and restarting it all. This "band-aid's" the problem for anywhere from 20 minutes to a few hours.  This past riday I installed a new router and replaced one of the 24 port hubs in an attempt to solve the issue. 3 hours later it occured again and I fixed it by shutting down and restarting everything. I am at a loss. Please help!
KjohnstingAsked:
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bbengsConnect With a Mentor Commented:
I would try going into the NIC driver on you XP systems and setting the speed (from Auto to 100 full) on a couple of NICs and see if the problem occurs on those NICs the next time that it happens across the board.  It may be that during high use on your network, your routers are negotiating there speed to much and are overworking the routers that you have.
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infotraderConnect With a Mentor Commented:
If this happens to ALL of your PC, regardless of which of the 3 hubs they are plugged into, then you might have a bigger problem than just the hubs or switches.

Why?  Because if you loose connection on one of the hubs, or even to your file servers, etc., instead of having the "balloon" pop up with the Local Area Connection, you might have another one saying that you'd lost connection to the network path, or something similar.  For example, if you have 30 XP machine seperated into 3 hubs, and 1 hub is dead, then you should have 10 computers with the ballon, and possibly 20 PC's with the "cannot access network drive" type of error message.

Another thing you might try to do is to replace the HUBS with SWITCHES.  Because HUBS are pretty primitive, it passes along a "token" throughout the entire network every time some packets is going through.  This can cause a lot of problems, including network storming caused by exccessive broadcast or hardware failure.  In some case the broadcast storming is so savere that the network might appeared "dead"

Finally, have you tried install some kind of UPS to these hubs/router?  Maybe something is wrong with your circuit or something, causing the electricity to shutdown periodically?

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KjohnstingAuthor Commented:
The hubs are switches (sorry). All networking equipment are backed by large APCs. Thasnks for your response.
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KjohnstingAuthor Commented:
When the issue was occuring, one of the hubs had all of it's LEDs flashing at the same time, while the other ones weren't flashing like that.  I went out and replaced that switch on Friday, 8/20/04 at 11am. The issue came about once more at 1:15pm that same day. Once again I shut down and restarted the networking hardware and the PCs. Since then we have had a skeleton crew working over the weekend and the issue has yet to come back since 1pm Friday. I am concerned that perhaps it is the router being overworked? Is there a way to check that?
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infotraderCommented:
As a test, you might want to remove the "hub" with the flashing LED out of the picture...    

If you can afford it... remove the hub and/or turn off all machines on that hub.  I have a feeling one particular device on that hub is having a lot of problems and/or infected with some kind of virus and/or trojan that is trying to broadcast and infect others.  This happened to one of my client.   As soon as I figured out which workstation was causint the trouble and removed it from the network, everything works.

If it were caused by a virus, however, then you might have multiple machines that's doing it.  From the looks of things, if that's the case, at least it's still in the same hub.

I am not so sure if the changing of the NIC speed is a good idea, however.  If anything, slowing down the speed on some of the machines might help the traffic congestion.

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KjohnstingAuthor Commented:
I solved the issue. I had the network daisy-chaining. That seems to have solved the issue. Thanks!
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cjkurtzCommented:
What do you mean about daisy chaining?  I am having a similar prom on a MAC network.
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KjohnstingAuthor Commented:
Switch C plugs into Switch B, plugs into Switch A...... In this case Switch A would be tier 1, B would be tier 2, C would be tier 3, so on...

As opposed to Switch B and C plugging directly into A. A would be considered tier one. B and C would be considered tier 2.

Ultimately you want one tier. That's why they sell those huge hp or Cisco modular switches that are physicall and logically one tier.
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cjkurtzCommented:
Thanks, I'll see if it applies for me.
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