Connection between Router and Switch keeps dropping to 100Mbit

M76

M76

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My old router died in a lightning related incident so I got a new one, and ever since then the connection speed between my router and a switch keeps dropping down to 100mbit. If I unplug the cable at the router side then immediately reconnect it then it goes back to Gigabit and remains so until it decides to drop again days or even weeks later.

I know the first thing to try is to replace the cable, but that will be the last thing I do because the cable is routed through a wall behind trim, under the doorsill etc. So I'm asking is there anything else I can do before going for that

The router is a Tp-Link Archer A8, I know it is probably not the best eva, but I assumed it couldn't be worse than the 12 year old linksys it replaced that already had one port dead on it before it completely died.
 
Any chance you can disable auto negotiation from either device? If not, if you have slack in the wire, maybe you can redo the ends as something to try before a new cable.

Given it takes a long time to drop, it's going to be a pain to test. Maybe the router has an auto reboot feature that will "fix" the problem. Or maybe you can do it with a smart outlet?
 
toast0 said:
Any chance you can disable auto negotiation from either device?
Click to expand...

WTF!? Horrible advice.
1) Auto speed/duplex is required for gig per standard. Do not hard code ever!
2) At no point in ethernet history has one hard coded one end of cable while leaving the other as auto. Both ends must match either auto/auto, or the case of 100BaseT and earlier only, hardcoded/hardcoded. Just in case in is not obvious the hardcoding must be the same on both ends.

OP If your device took lightning damage it is even more reasonable to presume cable problems. I would suggest that you try a new cable without routing it ie just loose on the floor running across the room for testing. If that works then you can replace and reroute.
 
So here's the thing. 100Mbit actually only requires 4 out of the 8 wires in the ethernet cable in order to work correctly. Gigabit requires all 8. So if any one of the 8 individual wires in the ethernet cable breaks, or you have a spotty connection at the jack on either end that blocks the signal on even just one wire, it will drop down to 100Mbit.

I had basically this exact same issue with a long run recently. It was frustrating because, similar to your case, occasionally if I unplugged it and plugged it back in, it would work at gigabit speeds for a while before dropping back down to 100mbit. Sometimes I'd have to re-plug it 15 times, while performing voodoo rituals, in order to get it to finally link-up at gigabit speeds. I figured, if it works at least part of the time, then it wouldn't be a cable issue, because then it wouldn't work at all, right?

After about a year of that, I decided to stop with the BS. I picked up a simple 2-part cable tester:

https://www.amazon.com/gp/product/B072LJYHKP

Sure enough, when I tested it, one of the 8 wires came up as bad. Despite it being inconvenient to replace the wire, knowing for sure what the problem was was still a lot better than constantly wondering if it was a wire issue, or a port issue, or an auto-negotiation issue, etc. As it turned out, when I went to replace the wire, there was in-fact some physical damage to the cable. There was just enough slack that I didn't have to fully replace the cable. In your case, if one of the wires shows as bad, you can always try replacing the ends first (if you haven't done that already).
 
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If lightning is really in play the nic in your pc is suspect as well. Run a temp patch cable to see if it fixes, if not then get a usb or pcie nic and try again. Or plug another machine into the line and see if behavior continues.

Sure it’s possible the router you have is bad but very unlikely with the behavior mentioned after an electrical event.
 
Nicklebon said:
WTF!? Horrible advice.
1) Auto speed/duplex is required for gig per standard. Do not hard code ever!
2) At no point in ethernet history has one hard coded one end of cable while leaving the other as auto. Both ends must match either auto/auto, or the case of 100BaseT and earlier only, hardcoded/hardcoded. Just in case in is not obvious the hardcoding must be the same on both ends.
Click to expand...

Ok fine. What I really mean is can you set either end to only offer gigE. That's within spec, and will probably keep the connection at gigE --- maybe with some drops at times... But, afaik, negotiating down to 100M when both sides support gigE isn't really to spec either. You're supposed to run at the highest mutually supported speed, there's no spec based support for measuring cabling quality or even that all pairs are present; negotiation happens at 1mbps on two pairs, smuggled into the OG 10M spec link pulses. It's very easy for spec based negotiation to fail horribly when the line is broken, which is why some devices/drivers cheat and change what they advertise.
 
toast0 said:
Ok fine. What I really mean is can you set either end to only offer gigE. That's within spec, and will probably keep the connection at gigE
Click to expand...

No, it absolutely is not in spec! Again both ends of the cable must match. Put aside the 1000 vs 100 .... Both ends of the connection must either be hardcoded to same specs or auto. Doing anything other will likely result in clocking issues as part of the auto spec is deciding which end supplies the clocking. Doing what you propose almost always ends up with each end at different speeds or duplexes at some point. It isn't even apparent there is problem until you attempt to pass significant traffic and you notice the horrible throughput.

As a side note .. We had an SE that practiced this behaviour you're espousing and over time he cost us 100s of man hours troubleshooting his installs when weeks later customer complain about speed issues. Eventually we figured out what was going and had the guy reprimanded and retrained. He kept doing the same shit and I had him fired.
 
Switch port could also have taken a hit during the lightning storm.
 
Nicklebon said:
No, it absolutely is not in spec! Again both ends of the cable must match. Put aside the 1000 vs 100 .... Both ends of the connection must either be hardcoded to same specs or auto. Doing anything other will likely result in clocking issues as part of the auto spec is deciding which end supplies the clocking. Doing what you propose almost always ends up with each end at different speeds or duplexes at some point. It isn't even apparent there is problem until you attempt to pass significant traffic and you notice the horrible throughput.

As a side note .. We had an SE that practiced this behaviour you're espousing and over time he cost us 100s of man hours troubleshooting his installs when weeks later customer complain about speed issues. Eventually we figured out what was going and had the guy reprimanded and retrained. He kept doing the same shit and I had him fired.
Click to expand...

Well yeah, that guy should be fired. If you're paying me, and I don't follow your rules, it doesn't matter who is right. Being able to follow clear rules correctly is part of what makes someone employable.

But you're saying I can't advertise I do auto-config, although my only supported speed is 1G full duplex and you advertise I do auto-config and 10/100/1000 plus all the half ans full duplexes (and yes, 1G doesn't have half duplex)... If our auto config stuff works, we should be able to find agreement and get there. Yeah, I know about the bad old days where setting configs would just do it and not send autoconfig anymore... then one side would say no autoconfig, so it must be 10M half duplex and the other side would be doing whatever was hard coded, and then bad stuff would happen... but it's 2023 and most things aren't that bad anymore --- forcing a speed changes what's advertised/accepted by the negotiation, but it's still negotiated.

I'm willing to agree that it would be better to set both sides, but probably it's an unmanaged switch and maybe the router doesn't have UI to adjust the negotation, I'd guess most people with a router and a switch can't set both sides.
 
First thing I'd do is try different ports on the switch and router. Next I'd get another switch, because gigabit switches are cheap. After that I'd just take a box of cat6, a crimper, and a couple plugs and set up a test cable. Or just buy a long enough cable. I have a crimper and tend to keep a box of cat6 and plugs around so for me it's cheaper an easier to just make a cable. Replacing a cable that goes through the wall is a giant PITA, but setting up a test cable is easy. Yeah you don't want a cable running across rooms, down hallways, etc. long term, but it's probably cheaper than swapping out the router.
 
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