issues over LAN

Hello
i have 40 meg fibre provided by plusnet using an ethernet cable from a pc into the router. All good with the PC and other wifi hardware. When i plug another pc into the router via an ethernet cable the speed drops to 1mb on both PCs. The wifi stays normal, sometimes, other times that drops aswell. i updated the drivers to the network cards etc and had the line tested which is good. Is this the router?
i would also note that the speed drops from 40meg to 1.5meg every 24hrs so i have to restart the router.

thanks in advance

Simon

Have you checked the traffic either PC is sending/receiving. Windows 10 task manager should let you identify which app is using a lot of bandwidth

Have you also checked that the IP address is unique on each PC

this /can/ happen if the 'new' pc has both wifi and lan connections so you get weird network loops

edit:
or even both 2.4 and 5gHz wifi connections.

Edited by ggremlin (Sat 15-Jun-19 21:22:07)

In reply to a post by ggremlin:

this /can/ happen if the 'new' pc has both wifi and lan connections so you get weird network loops

Interesting - I've done this with several laptops without thinking, and never encountered any attributable problem.

Tried different ethernet cables?

It doesn't cause an issue, as each connection will have its own IP address.

If you remove the original PC and only plug in the newer PC, does the speed remain at 1 meg or does it go back to 40 meg?