Strange problem with Ethernet switch
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Posted by ohaya on September 7, 2004, 12:57 pm
Please log in for more thread options I've been wondering for awhile about a problem that I'm having with an Ethernet switch, so I hope that someone here can offer an explanation. The switch is a Gigafast EE500-S. It's a 5-port 10/100 switch. In my network, I have a Netgear router with a 4-port 10/100 switch, built-in to the router, that connects to my cablemodem provider. I have a cable going from one of the ports on the Netgear to the wall in one of the rooms in my house. If I plug a cable directly from the wall to the uplink port of the Gigafast switch, I can ping my router and external destinations from any PC that's connected directly to the Gigafast, but I get about 50% timeouts. If I ping any other computers directly connected to the Gigafast from another computer on the Gigafast, everything is ok. This is regardless of how I configure the NICs on the PCs connected to the Gigafast (10 HDX or FDX, 100 HDX or FDX). I kind of puzzled over this for awhile, but then, instead of connecting the Gigafast uplink directly to the wall, I tried connecting an old 10Base-T hub between the Gigafast and the wall (i.e., Gigafast uplink port to hub port via crossover cable, and then hub port to the wall), and lo and behold, when I ping from any PCs connected to the Gigafast to either my router or external destinations, no more timeouts. I would love to eliminate the need for this "in-between" hub, but I can't figure out why it's needed to get from the Gigafast to the router. Can anyone here explain this?? Also, is there any way to allow me to connect directly from the Gigafast to the wall, to the router? Thanks, Jim | |||||||||||||||||||||||||||||||
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Posted by J. Clarke on September 7, 2004, 1:47 pm
Please log in for more thread options Sounds like a duplex mismatch between the Gigafast and the Netgear. Try shutting _everything_ down then connecting the two, then power them up, then power up the rest of your system. If that doesn't work, it could be a bad cable that will carry 10 Mb/sec but not 100. Try running a known-good cable directly between the two and see if the problem recurs. If so, then before I wasted any more time troubleshooting it I'd replace the Gigafast switch with a Netgear and see if it was an incompatibility. >
> > Thanks, > Jim -- --John Reply to jclarke at ae tee tee global dot net (was jclarke at eye bee em dot net) | |||||||||||||||||||||||||||||||
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Posted by ohaya on September 7, 2004, 9:57 pm
Please log in for more thread options rom the Gigafast to the wall, to the router?
>
> Sounds like a duplex mismatch between the Gigafast and the Netgear. Try > shutting _everything_ down then connecting the two, then power them up, > then power up the rest of your system. If that doesn't work, it could be a > bad cable that will carry 10 Mb/sec but not 100. Try running a known-good > cable directly between the two and see if the problem recurs. If so, then > before I wasted any more time troubleshooting it I'd replace the > Gigafast switch with a Netgear and see if it was an incompatibility. John, Thanks. I'll give that (powering the router and switch up first by themselves), but it is the cable not being able to carry 100 Mbps, shouldn't the switches (both the one inside the Netgear and the standalone) be able to negotiate that? Both of these switches are *suppose* to be "10/100" switches... Jim | |||||||||||||||||||||||||||||||
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Posted by J. Clarke on September 7, 2004, 11:03 pm
Please log in for more thread options ohaya wrote:
> rom the Gigafast to the wall, to the router?
>>
>> Sounds like a duplex mismatch between the Gigafast and the Netgear. Try >> shutting _everything_ down then connecting the two, then power them up, >> then power up the rest of your system. If that doesn't work, it could be >> a >> bad cable that will carry 10 Mb/sec but not 100. Try running a >> known-good >> cable directly between the two and see if the problem recurs. If so, >> then before I wasted any more time troubleshooting it I'd replace the >> Gigafast switch with a Netgear and see if it was an incompatibility. >
> > John, > > Thanks. I'll give that (powering the router and switch up first by > themselves), but it is the cable not being able to carry 100 Mbps, > shouldn't the switches (both the one inside the Netgear and the > standalone) be able to negotiate that? The quick answer is no. Fast Ethernet devices communicate with each other at 10 Mb/sec to negotiate the capabilities of the devices at each end of the cable and then switch to the highest performance level that both support. All the negotiation though occurs at 10 Mb/sec. They do no testing of the cable, and they have no fallback modes. If both devices support 100 full duplex then that is what they set themselves for and if the cable isn't up to it then communication is impaired in one manner or another and to a greater or lesser degree depending on what's wrong with the cable. > Both of these switches are
> *suppose* to be "10/100" switches... > > Jim -- --John Reply to jclarke at ae tee tee global dot net (was jclarke at eye bee em dot net) | |||||||||||||||||||||||||||||||
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Posted by M.C. van den Bovenkamp on September 8, 2004, 5:02 am
Please log in for more thread options ohaya wrote:
> Thanks. I'll give that (powering the router and switch up first by
> themselves), but it is the cable not being able to carry 100 Mbps, > shouldn't the switches (both the one inside the Netgear and the > standalone) be able to negotiate that? Both of these switches are > *suppose* to be "10/100" switches... No. Autonegotiation does not check for cable quality. It just checks what the capabilities of the other end are, and will negotiate the best combination. Whether the cable can actually support that is something else entirely. I agree with the previous poster that a duplex mismatch is the most likely problem, with a split pair somewhere in the path a close second. Regards, Marco. | |||||||||||||||||||||||||||||||
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>
> I've been wondering for awhile about a problem that I'm having with an
> Ethernet switch, so I hope that someone here can offer an explanation.
>
> The switch is a Gigafast EE500-S. It's a 5-port 10/100 switch.
>
> In my network, I have a Netgear router with a 4-port 10/100 switch,
> built-in to the router, that connects to my cablemodem provider. I have
> a cable going from one of the ports on the Netgear to the wall in one of
> the rooms in my house.
>
> If I plug a cable directly from the wall to the uplink port of the
> Gigafast switch, I can ping my router and external destinations from any
> PC that's connected directly to the Gigafast, but I get about 50%
> timeouts.
>
> If I ping any other computers directly connected to the Gigafast from
> another computer on the Gigafast, everything is ok.
>
> This is regardless of how I configure the NICs on the PCs connected to
> the Gigafast (10 HDX or FDX, 100 HDX or FDX).
>
>
> I kind of puzzled over this for awhile, but then, instead of connecting
> the Gigafast uplink directly to the wall, I tried connecting an old
> 10Base-T hub between the Gigafast and the wall (i.e., Gigafast uplink
> port to hub port via crossover cable, and then hub port to the wall),
> and lo and behold, when I ping from any PCs connected to the Gigafast to
> either my router or external destinations, no more timeouts.
>
>
> I would love to eliminate the need for this "in-between" hub, but I
> can't figure out why it's needed to get from the Gigafast to the router.
>
>
> Can anyone here explain this?? Also, is there any way to allow me to
> connect directly from the Gigafast to the wall, to the router?