Asus RT-AC66U randomly switches to 100Mbps on LAN

Soldato
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I have an Asus RT-AC66U with the Merlin 380.70 firmware, connected to it is my Virgin router (modem mode) and then 3 PCs and a PS4 Pro on the ethernet ports with Cat 6a cables. At random, any of the ports will randomly drop to 100Mbps instead of 1Gbps. Forcing the PC network adaptors to negotiate at 1Gbps does nothing. The only fix seems to be forcing the router to re-negotiate until it connects at 1Gbps, the easiest way I've found to do this is to just unplug and reinsert the ethernet cables until it eventually connects at 1Gbps.

Unless I'm missing something, the two most likely options are either all my ethernet cables are faulty or it's something to do with the router. Has anyone had any experience with problems like this? I'd appreciate some thoughts and advice.
 
Soldato
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I'd guess bad cable too, possibly been crushed under a door or something?

The cables have never been damaged in any way. However, my best and most hopeful guess is bad cables too. So I've ordered a replacement Cat6 for the PC that needs the shortest cable and will test that.
 
Soldato
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What happens with one device connected direct to the modem? Remember to take appropriate precautions.

The router is connected to the modem and that's never dropped under 1Gbps. However, that is also the shortest cable at 50cm or 1m, I can't remember. I'm hoping that it's due to the quality of the cables and that such a short cable is more forgiving, hence why it's not been a problem for the router.

Either way, I'll replace the HTPC cable and see what happens.
 
Soldato
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I had a connection between 2 switches that dropped to 100mb randomly, re-plugging the cable would fix it but then it would drop again sometime later. The cables hadn't been touched and no damage was visible. I cut the RJ45 off each end and reterminated, it's worked fine ever since.

Hopefully the replacement cable fixes it for you.
 
Soldato
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I have an Asus RT-AC66U with the Merlin 380.70 firmware, connected to it is my Virgin router (modem mode) and then 3 PCs and a PS4 Pro on the ethernet ports with Cat 6a cables. At random, any of the ports will randomly drop to 100Mbps instead of 1Gbps. Forcing the PC network adaptors to negotiate at 1Gbps does nothing. The only fix seems to be forcing the router to re-negotiate until it connects at 1Gbps, the easiest way I've found to do this is to just unplug and reinsert the ethernet cables until it eventually connects at 1Gbps.

Unless I'm missing something, the two most likely options are either all my ethernet cables are faulty or it's something to do with the router. Has anyone had any experience with problems like this? I'd appreciate some thoughts and advice.
I've had a very similar problem using Merlin on a AC68U with SuperHub in modem mode. Every now and then I noticed my speed would drop to 100Mb.

I fixed it by replacing the cable running to my PC - which is the only wired equipment I have. I've never had the issue since.
 
Soldato
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What about those Ethernet testing kits?

The type you are referring to literally test for continuity, they’ll tell you if the cable has a break or is wired up incorrectly, that’s it. If it’s dripping to 100Mbit then neither of those are relevant.
 
Associate
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ive had this before, i cleaned the contacts in the ethernet port and cut off the rj45's and fitted new ones and it fixed it.
 
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