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bdubs85
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Posts: 44
Joined: Fri Sep 07, 2018 4:30 am

Random wired link down

Fri Mar 06, 2020 9:17 pm

I have recently changed my network config and noticed a random link down with no error with a link up 4 seconds later that mostly occurs overnight. For example, last night link downs occurred more often than normal but at 02:26:01, 03:22:06. 04:07:10, 05:34:12, 06:52:49, 07:05:34, and then uncharastically just recently at 12:36:52. It is probably a 50' length of cable that is ran under the house, but cable testing shows "link ok" and that it is working fine at gigabit speeds. I previously had the 4011 set as a capsman and then the 2011 and wAP ac set as CAP devices to simplify management when I noticed this link down problem. I then reset and configured the devices manually to see if this was some configuration problem (just plain vanilla bridge with DHCP client), but the link downs still happened. I then bought a RB260GSP switch just in case it was a problem with the RB2011 (I didn't have any other gigabit capable routers for my other devices at the time), but the link downs continued to happen even with the switch.

I've tried turning off Auto Negotiation since the links are gigabit, loopback protection on and off, and various other things. There are no VLANs at this time, just bridges on each router and hardwired cat5e/cat6 links between all devices. I've lowered the 4011 bridge priority to 4000 to ensure it is always root with RSTP. I'm not getting any sort of explicit error messages on any routers when this occurs, and it is so random that I can't really track down any particular thing that would trigger it such as an ARP change or something. I've also tried changing the ports on the 4011 and 2011 to ensure that there isn't some weird switch chip miscommunication.

On the RB260GSP switch, it lists on port 1 Rx (coming from the 4011) FCS Errors: 7 and Tx Pauses 174, so my first thought was running new cable directly between devices to rule out bad connections.

Any ideas on what might cause this sort of link down thing or how to track down what is causing it?
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leoservices
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Re: Random wired link down

Sat Mar 07, 2020 5:37 am

It seems to me to be a problem with the cable, if possible do a "Certification" test with FLUKE DSX-5000 or another scanner that reports external noise, noise between pairs, etc. Connector may also have some bad intermittent contact.
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Leonardo Vieira
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bdubs85
newbie
Topic Author
Posts: 44
Joined: Fri Sep 07, 2018 4:30 am

Re: Random wired link down

Sun Mar 08, 2020 2:10 am

I don't have an external tester unfortunately, I was just going based on the mikrotik cable tester and performance.
 
Kapenaar
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Joined: Thu Aug 18, 2016 12:05 pm

Re: Random wired link down

Sat May 23, 2020 10:11 am

You may think this is a stupid answer. I had same issues on multitude of MT's. Do a proper EARTH on your routers and your problems will go away.
 
Kapenaar
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Posts: 4
Joined: Thu Aug 18, 2016 12:05 pm

Re: Random wired link down

Sat May 23, 2020 10:13 am

To everyone experiencing linkdowns, as a rule of thumb; FIRST do proper earthing and see if you still require any other solutions. For linkdowns, earthing is the anti-biotic! (And if you wonder, I have working with MT since 2006).

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