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I have this Netgear 5-port gigabit switch. You know, one of those rounded white models. Well, it worked well in combination with a Netgear DSL router for a few years.

The network topology is relatively simple: the DSL router with one PC connected to it via ethernet, 2/3 devices connected via wi-fi, and the switch connected to it as well. The switch is connected to 2 other PCs, one of which is almost always off.

Everything used to work very well until I noticed a few weeks ago a degradation of the Internet connection speed, down to around 1MBit/s instead of around 4. I blamed the DSL provider, as one would naturally do. Today I took the time to test the connection from the other PCs, and it is way faster when not passing through the switch but connecting directly to the DSL router.

I noticed that with all PCs off, on the DSL router the led of the connection between it and the switch always, constantly blinks. I'm assuming the switch is broken and for some reason it still works but with a degraded performance, which is a bit odd in my opinion.

I'm resolute about replacing the switch, but I was wondering if what I'm seeing makes sense at all before wasting money.

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I've seen bad ports and bad cables. Have you tried mixing and matching to ensure it's not just one of these? – uSlackr Feb 2 '12 at 19:09

The answer is yes, in the sense that anything can break down, and electronics are no different to anything else.

What is very unlikely is that it would degrade without any obvious cause. You should look to identify the problems, such as packet loss or packet errors, that the switch is causing to isolate blame there.

Otherwise a cause like an improperly plugged or damaged cable, or a modem fault, or an upstream fault, or network misconfiguration, are just about as likely.

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I used Windows' performance counters and verified that through the switch I get loads of "Packet Received Errors", while directly to the router the number does not increase. So it seems the switch is corrupting packets. – Dario Solera Feb 2 '12 at 19:03
A working switch should have zero, or very, very close to zero, errors of any sort. So, yes, that points to the broken switch, or a broken cable. Check different cables, and different switch ports, and see if they change the behaviour - but otherwise looks like you were right, and the switch is bust. – Daniel Pittman Feb 2 '12 at 19:56
Switch replaced, everything is fine. – Dario Solera Feb 3 '12 at 16:55
up vote 1 down vote accepted

I'm answering my own question because I replaced the switch and everything is back to normal. So the answer is, yes a broken switch can slow down the network connection simply because it corrupts data.

Bonus note: my wireless mouse, that was acting strange, now works perfectly, so it seems the broken switch was also generating electromagnetic noise.

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+1 because I keep getting answers like "these switches work fine we use them" from resellers. I don't buy large volumes but I already encountered multiple situations where switches were the problem. Usually you can simply see the switch freeze or "restart". But when the data passing through the switch is corrupted user usually don't notice the problem. Until the network is tested that is. Overheating is often the aggravating factor if not the cause of malfunctions. – Coyote Oct 29 '12 at 14:10

In theory anything is possible but I've never seen that kind of failure mode in a switch... usually it will just stop working entirely.

As the previous answer said, I'd look for a physical problem like cabling. Plug your computer into a different port on the switch and see if it gets better, or try a new network cable.

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