Ethernet problem with my iMac (High Sierra)

[Synchronyme]

Hi everyone,

I've got an issue with my internet connection : once in a while (like 3-4 times every day), my internet is very slow and when I test it with a ping, I see that about 50% of the parquets are lost (request timeout).

That only happen on my iMac (10.13.5). My Macbook (WiFi) and my other PC with Linux have zero issue. Also it doesn't happen if i turn the WiFi on. It's only when I'm connected via Ethernet. I also tested multiple Ethernet cables but the problem keeps happening.

Most importantly, if I then remove the Ethernet cable and put it back on, the connection is perfect again (0 paquets lost). If I do nothing, the connection issue can last for 5-10 minutes, sometimes more, then disappears.

What could cause that ?

 

[kschendel]

Are local pings slow as well, or just pings to a remote computer?

If local pings are slow, I'd normally suspect the cable. If you have tried several known good cables, it could be the ethernet hardware in the computer itself.

 

[Fishrrman]

I just read another thread a few minutes' back, from a user who was having "ethernet problems".

He (at first) suspected his Mac (either hardware or software).
Further investigation led to the diagnosis of a bad internet modem/router (supplied by his ISP).
Replacing that "fixed" things.

So... before you "blame the Mac", could it be something else in your current setup?

A test you might try:
1. DISCONNECT the ethernet connection (temporarily)
2. Use wifi only for now
3. Run this way one or two days
4. Are you still seeing packet losses?

The idea here is "to remove ethernet" from the equation and see if the problem persists with wifi. If it does, it's not "ethernet"...

 

[monokakata]

Do you have an all-in-one modem/router, or separates?

If separates, one thing you could do would be to plug directly into the modem's ethernet port, and see what happens. That would allow you to exclude your router, just in case something weird's happening at the router itself.

Similarly, if you have an all-in-one but either have a router lying around or could borrow one, you could disable the router on the all-in-one (it's pretty easy to do on most of them), go through the temp router, and see what happens.

And is there a switch involved? If so, bypass it temporarily.