Question Speed & Duplex Disconnect

Jul 4, 2021
I have a Cat 6 50ft ethernet cable. My internet speed is 400mbps download and 20mbps upload. I switched my speed and duplex setting from auto negotiation to 1.0Gbps because I was being limited to 100mbps. It worked for about 3 days no issues, computer turned off about once a day. Then I came home today and it says Network Cable unplugged, checked the router, it handles up to 1Gbps for each port.


Aug 20, 2020
It's almost always the cable or more likely, the RJ45 connectors.

The fact that it won't auto-negotiate to 1gbps means that the line is 'dirty' or one of the pins aren't making positive contact.

Here are a few things I've done before that works... YMMV.

  1. Unplug and re-plug the RJ45 connectors and make sure that they're snug in their ports
  2. Use a copper steel brush and lightly brush the fingers on the RJ45 plug. This can help remove oxidation or dirt
  3. If the cable was DIY'd, try using a crimper to further push down on the pins so they bite the cables properly
  4. Cut off the RJ45 connectors and crimp in a new one
Reactions: bill001g
Yep, any cable that was working at gigabit and then went to fast ethernet is probably a bad cable. I've seen this happen on some of my oldest cables once they got past a certain age--just replace the cable with a good one, and watch out for the fakers because there are more of those than legit ones. Best way to get a legit one is to buy it at a local store since they would have too many angry customers in their face if they sold junk.