Question ASUS RT N12-D1 mystery: multiple ethernet port failure?

Sep 19, 2020
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I have an ASUS RT N12-D1 which has been working flawlessly for a long time (a year-ish). It's the house router, providing wifi and also supporting wired (RJ45 cable) ethernet clients on 3 of its 4 ports. The clients are: a Synology NAS box and two desktop computers with ASUS mobos (a MAXIMUS GENE and a HERO). Everything has been working great for months.

Then I went away for about 3 weeks. When I came back, the two desktop machines were reporting "Ethernet cable unplugged." But the NAS box was still online and working fine.

Greatly puzzled here. Tried swapping one desktop RJ45 cable to the unused router port. No result. Tried hard power cycle on router. No result. Switched OS on one of the desktops (OSX to Win10). Just as dead under Win10 so presumably not an OSX driver issue. No lights on ethernet port on back of mobo when plugged in.

I don't understand why the NAS port is still working, wifi is still working, yet (apparently) 3 other ports are dead. I'm a little afraid to swap one of the desktops onto the NAS port in case that somehow breaks that one too :) The web interface to the ASUS router seems pretty shallow, i.e. no hardware diagnostics that I have yet found, no hardware port monitoring or status? I do see that the router sees only one client on an ethernet port.

If the problem is on the mobos of the desktop machines then I don't understand how they could both fail simultaneously. If the problem is at the router then I don't know why those two (three?) ports would fail together while the NAS port was untouched.

The desktop machines are on longish RJ cables (but well within spec) while the NAS is on a shortie, being co-located with the router. That's the only difference. The unused port has never, afair, been connected to anything until today when I tried the swap. So I could come up with a theory about long RJ cables and a lightning strike nearby, but that wouldn't explain the unused port which never had any cable connected.

Does this router have a reputation for losing its RJ ports due to power failures? Our local power is not super reliable -- we expect interruptions at least once a month and sometimes more frequently. One of the ASUS mobos has been in service over 2 years with wired ethernet, with never a hiccup, through many a power hit. The other is only about 7 months in service but has never had an ethernet issue till now. Is it really reasonable that both of them would die within the same pretty small timeframe (while I was away)?

I'm seriously puzzled (and inconvenienced by losing network connectivity for two production machines -- neither of them has wifi capability). If anyone has suggestions as to where the blame is likely to lie -- should I replace the router? -- I'm all ears. Head scratching here, not to mention a bit of cussing.

Diagnostic suggestions gratefully welcomed, anyone...?
 
Okay, so just to preface--switch ports can die and leave the rest of the switch working fine. I have an older 16-port dlink that has only 7 ports working now, lol, and it still does work.

That being said, there's almost no harm in moving the synology cable to the other ports to test them. There is a chance that by some weird nearly impossible scenario, the synology's port would be fried or the remaining working port would stop working, but I highly doubt it. Still even diagnosing this and confirming that the other ports don't work doesn't really solve the problem, so maybe we can just solve the problem since it's dirt cheap--which is to buy a switch and plug it in the working port that the nas is using and then connect everything to that new switch. That should have you up and running in minutes. And these simple 4/5/8 port switches are easily found locally, so you should be able to go get one right now and fix this in under an hour. :)
 
Sep 19, 2020
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Thanks for the thought. I in fact had a little D-LINK switch lying around unused, which I dug up and used to check this out. Plugged it into the NAS port, connected the NAS to one of its other ports, all blinking happily. Plugged in one of the "no cable" desktop computers and aha, no lights, no connection. So the problem I think we can safely say is not with the router. I'll do yet more tests to reassure myself of this absolutely, but so far I think the router is innocent.
 
Great diagnostic work! Depending on where those long runs go (in wall, direct cable, etc), I would suspect the cabling before the desktops.

If possible, move the desktops near the dlink switch/router and run a test with a shorter cable. That will pretty much rule out the desktops one way or another. :)
 

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