Strange problem with Ethernet switch

Hi,

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

Reply to
ohaya
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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.

Reply to
J. Clarke

rom the Gigafast to the wall, to the router?

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

Reply to
ohaya

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.

Reply to
J. Clarke

Marco,

Thanks for the clarification. Unfortunately, the cable is "in the wall", so I can't do much about it. I tried the powering off/on, but still the same results. I might to see if I can find a different switch that might work.

I know that the Gigafast switch is unmanaged, but is there any possibility that the port on the router might be configurable, i.e., so I could try to force it to say, half-duplex?

FYI, I just noticed when I plug the cable from the wall directly into the Gigafast switch, the FDX and 100 lights are lit solid, and the LNK/ACT light is constantly blinking fast. According to the manual I found, this is suppose to mean that there's data activity.

Jim

Reply to
ohaya

Not on a Netgear. Netgear makes some Layer 3 managed switches for a thousand bucks or so but they don't make any 4 port routers with management on the switch ports.

You could spend 60 bucks for a couple of SMC 9452TX network adapters or another built on the Marvell Yukon chipset and run the cable test software they provide on the suspect cable--it uses the signal processors on the gigabit chip to do many of the tests that a cable scanner would do. If you find out for sure that the cable's bad you'll have a better idea what you're up against. Or if you're in the Hartford/Springfield area and have beer send me an email and I'll bring my Fluke over.

Reply to
J. Clarke

Robert,

I worded that unclearly. Yes, there's a wallplate, and I have a male-male patch cable connecting from the wall to Gigafast switch (or the hub).

So the config that works:

This cable is "in the wall" | V Router Wall Hub Switch PCs (Bsmt) Plate

And the config that I'm having problems with:

Router Wall Switch PCs (Bsmt) Plate

Sorry if I was imprecise. Jim

Reply to
ohaya

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.

Reply to
M.C. van den Bovenkamp

Depends. If it is possible, the docs of your Netgear should mention it.

Do the Netgear and the Gigafast have LEDs to indicate duplex? If so, you could see whether they agree on things.

If they do agree on duplex mode (either half or full), a botched cable is the most likely problem, and if you can't fix it, running the link at

10Mbps is the only option. Split pairs will do that to you (link that works fine at 10, but doesn't work or works badly at 100).

So the Gigafast has LEDs. Does the Netgear, and do they agree on duplex mode? Speed is OK, or the link wouldn't work at all.

Regards,

Marco.

Reply to
M.C. van den Bovenkamp

If you have a split pair, the switch may think the cable can do 100, but it can only in one direction. The autoneg works on _advertised_ capabilities, not measured.

-- Robert

Reply to
Robert Redelmeier

Actually, so long as the cable is good quality Cat5 not overpulled or kinked, split pairs can be fixed.

"Cable from the wall directly" ... do you mean there isn't a jack & patchcord? Somebody crimped a plug on cable in the wall? A very likely cause of split pairs.

-- Robert

Reply to
Robert Redelmeier

Much clearer! Maybe the router and/or switch expects a crossover cable or an "uplink" port to be used. The hub does the XOVER. Try a replacing the patch-cable with a crossover cable.

Either that or the router or cable won't do 100 MHz correctly. The cable in the basement at the router end, it is also a factory patch-cord?

-- Robert

Reply to
Robert Redelmeier

No, that can't be it. In that case the link wouldn't even come up, and that's not his problem.

What I haven't yet seen an answer to, do router and switch agree on duplex mode? A duplex mismatch is still a possibility. That, or a miswired cable.

Regards,

Marco.

Reply to
M.C. van den Bovenkamp

M.C.,

Sorry, I might've missed that question.

Yes, both router and switch have FDX and 100 lights lit solid. The LNK/ACT light on the switch is fast blinking (too fast, like it's noise) when I try this.

Jim

Reply to
ohaya

Robert,

The switch has two connectors for port 1, a "normal" and an "uplink" connector. If I plug the cable from the wall into the "normal" connector on the switch, I get no lights. If I plug the calbe into the "uplink" connector on the switch, I get FDX and 100 lights solid, and fast blinking LNK/ACT light.

I have a new switch (an SMC 16-port 10/100) on its way, and I'll give that a try when it gets in. If that doesn't work, I guess I'm stuck with the hub+switch configuration (seems like such a waste of the hub though).

Jim

Reply to
ohaya

Yes, as pointed out by another poster, a crossover mis-match would result in not working at all.

This could well be a split pair (data errors). Are there _any_ home-made crimped plugs in the cabling?

-- Robert

Reply to
Robert Redelmeier

Try another switch, its possible that switch is damaged.

I had a customer's switch take a dump after a bad lightening storm. Same problem...it worked, but bad packet loss.

Reply to
CJ

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