Slow LAN speeds when using wired connection

[#1]

I have fibre broadband and if the router is plugged directly into the modem I can get 145 Mbps download. However, I have a wired LAN connection in the office upstairs but can only achive 94 Mbps download. I have tried upgrading the LAN modules to Cat 6 and ethernet cable to solid rather than stranded wire but it makes little differnece. Is the amount of loss expected for a LAN cable run of less than 15 meters? How can the wired LAN speed be improved?

[#2 · Accepted solution]

@och2024 

This sounds like a classic case of something on your network limited to 100Mbps. I would start by checking out your Ethernet cables. I have done some experimenting recently.. For 1GHz you need all 8 cores connected but only 4 for 100Mbps. If one of the cores not used for 100Mbps becomes disconnected then it automatically reconfigures to 100Mbps. It’s either one speed or the other, the network doesn’t slow to an intermediate level.

A cheap tester is a worthwhile investment.  https://www.amazon.co.uk/Network-Cable-Tester-RJ45-Ethernet/dp/B08RNDBQRX/ref=sr_1_1_sspa?keywords=e...

[#3]

I've tried connecting all 8 cores and there is no difference. Yet if I use a long patch lead the speed greatly improves.

[#4]

@och2024 

Have you checked that the Ethernet cable that you are using is at least CAT 5E. CAT 5 or lower is not suitable for 1000Mbps.

The maximum length of cable for CAT 5E at 1000Mbps is 100M.

[#5]

It's all sorted now. It was a loose connection on pin 8. Cable used was cat 6.

[#6]

@och2024  Good result thanks to @Baldrick1 suggesting an ethernet cable problem, it can happen quite often, I have been caught out by Cat 5e patch cables with only two pairs so only good for 100Mbps.☹️