Aug 31, 2020
Recently I built my first PC with these specs:

Ryzen 7 3700x
Rx 5700 xt
16 gb DDR4 corsair vengeance pro ram
ROG STRIX B450-F motherboard

At first the PC would auto negotiate, but after a few days when the speed was set to auto negotiate the PC would disconnect from the internet. Now it only works with 100 mbs full duplex and 100 mbs half duplex, and for some reason the 100 mbs half duplex is faster than the full duplex.

I am new into computers, so any help to fix this problem would be appreciated.


Welcome to the forums, newcomer!

Make and model of your PSU? What is the maximum bandwidth for your connection(that you're paying for)? Might want to check and see if you have any BIOS updates pending for your motherboard. Do you have an intermediary component between your desktop and your ISP, like a router?
There are very few things that can cause this a bad cable being the most common cause. The other causes are bad ports in the router or PC which you can't really fix so you need to hope it is the cable.

Leave the setting on auto. To use any other setting you must also set the router port and that is not possible on most consumer equipment. The router will be on auto and get confused when it does not receive the proper negotiation from the PC.

This should just work. It is done by the hardware chips themselves. There is not much bios/driver stuff other than forcing it to run some speed.

It would be nice if cable would just not work at all when they are bad. It is very common for a cable to get one wire that is just slightly loose in the end and as the heat changes you get strange results.

Although you could try to cut off and recrimp the ends on it tends to not be worth the costs unless the cable is very long or it is in the wall where you can't easily replace it.

When looking for a replacement cable watch out for all the fake cable being sold. You want a cat5e cable that is pure copper (no CCA) with wire size 22-24 (no flat or thin cable). You can get cat6 if it cheaper but it won't run any faster.