@Kevin_Z 

Hello.

Thanks for getting back to me. I have tested with two other devices that both have gigabit ports, and the result is the same. They only connect with 100/100Mbps.

Hello.

I think I might have found the issue. It seems the two cables I tested with have suffered some damage, and as a result does not connect with all 4 pairs, hence giving only 100/100. This is a cable I had been using only a week prior with full speed, so I made the assumption it was working fine, which I apologize for. 

I found an unused cable which immediately provided me with 1Gb to my test laptop as well as a secondary device, so the router is perfectly fine, and the issue is located at my equipment end. 

Thank you for taking the time to help me with this situation, and once again apologies for taking up your time.

  @copyrght 

hello,

I am having the very same issue as you and others here. I have 1000mbps on the WAN port but only 100mbps on LAN. I set to force negotiation to 1000mbps but there is no LAN options.

This just started about a week or so ago. I've changed cables to try several cat5e but all of them have the same issue. There was a firmware update earlier when I first noticed the problem is in the router but after updating I still am limited to 100mbps

  @Kevin_Z 

How on Earth am I going to check my internet speed without the modem attached? This advice makes no sense. I have been having no troubles with 1000mbps speed using this router for months. It only stopped working a week or two ago and I just figured out the router is the problem a couple of days ago. I connected my old TP-Link AC1750 router and everything is back to 1000mbps using that router. The only thing is, I replaced that router with this one for the WiFi 6 because the old one doesn't handle traffic worth a damn. 

Anyway, If you have a reasonable solution that makes sense, please let me know. I think I'm just going to buy an industrial grade router next month and put consumer grade equipment in my rearview mirror forever. What I'm positive about, is that I will not be buying any TP-Link routers in the future. Control options are extremely limited and the routers clearly aren't capable of handling the amount of devices in a modern household. I don't even have many IoT things in my home (maybe 20 at any given time) and this is the second TP-Link router that stopped doing it's job after a few months. 

  @Kevin_Z 

Hi, I have been facing the same issue for several weeks now. I have tried everything mentioned in the thread but it is of no help. Can you please help me out with this?

This has been causing a lot of issues for my WFH.

  @Kevin_Z 

Hi,

Please find the description below:-

Model: Archer AX23 v1.20

Troubleshooting
I have changed the Negotiation Speed to 1000 mbps full duplex, but that doesn't change the lan port speed.
I have tried with different ethernet cables such as Cat 5E, 6 and 7. So the ethernet cable shouldn't be a problem.
Resetted the Router through software/admin page and also performed a hard rest, with the reset button.
Tested by replacing with my old Archer C7 V2, and I get Gigabit speeds from that using the same cables and adapters.