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We recently had a very strange problem. Two users share a 1gbps switch, and their network connection has been getting worse and worse (it does not disconnect, but has gotten REALLY slow, down to bytes/second). We tried three different known-good switches, with no luck, even with only one person plugged into the switch, and even when forced to 10mbps. The offices around theirs (all using 1gbps switches) have no problems.

The thing is, when we hook either of them up directly to the wall, the connection is fine! Knowing that with only one computer, a hub is basically the same as a repeater, I replaced their switch with a 10mbps hub - presto! No more problems.

My question is, what possible circumstances could cause a hub to work when a switch doesn't?

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Are the 1 Gbps switches managed? If so, are there log events or usage details that could be obtained? –  Dave M Jan 15 '10 at 15:41
    
amazon.com/Linksys-SD2005-5-port-Gigabit-Switch/dp/tech-data/… I see reviews stating that, like many of our Acer monitors, this model of switch is plagued with leaking capacitors ( en.wikipedia.org/wiki/Capacitor_plague ) –  BlueRaja Jan 15 '10 at 16:02
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Did you try other switches? Did you try this switch at other locations? –  mouviciel Jan 15 '10 at 16:14
    
To amplify mouviciel's point; you've changed too many things by going from a Gig switch to a 10 Meg hub ... Try another gig switch; try a 100meg switch. As Doltknuckle says below, you need to carefully go about isolating where exactly the problem is. –  Adrien Jan 15 '10 at 18:07
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2 Answers 2

up vote 5 down vote accepted

To answer your question, the only times a hub works better then a switch is when you have bad hardware or incompatible hardware. The first is relatively easy to test, but incompatibilities can be difficult to find. I have run into switches that just don't like communicating with particular switches. Try switches that are different models and manufactures and see if that makes a difference. The duplex mode (Full or Half) used can also make a difference so make sure you try both communication methods.

In your situation, I would suggest you start from something called a "working set". That means you build a chain of devices that work, then swap out individual parts one at a time. To start, you need to identify the components in the chain. This is usually everything between the troubled computer and your network backbone. In this case, the components that could be having problems are as follows:

  • The office computers
  • The cable connecting to the "switch/hub"
  • The "switch/hub"
  • Cable connecting to wall
  • Patch from wall to building switch
  • Building switch

I would go into one of the other offices and plug swap a known good computer for a bad one. If it works fine, then change out the cables. If that works, swap out the switch in the room. If that works, swap the port used at the building level switch with the one used by the other office. If that all works, move all the currently working parts back into the "bad" office and try it again.

If it dies anywhere along that chain, then you should be able to figure out what it broken. Keep in mind that your building switch (device on other end of wall plate) could have a bad port and may be only to work with a hub.

Hope this helps

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+1 nice, detailed answer. –  Tadeusz A. Kadłubowski Jan 15 '10 at 18:10
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Checkmark for hardware problem, capacitor plague strikes again. For some reason plugging the switches into that room killed them (but the power is stable enough for most other electronics) –  BlueRaja Jan 18 '10 at 21:57
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Maybe the hardware at the other side of the wall is having trouble negotiating the connecton with the swiches but not with the hubs. I found one time that one switch negotiated the connection at full duplex and the other one at half and had LOTs of weird problems.

The better way to diagnostic the problem I can think of is with a fluke device called Net Tool. You can find it here

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