Sudden network speed drop from 1Gbps to 100Mbps on Fedora 40

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1

Hello everyone,

I’m experiencing an issue with my integrated network card (Realtek RTL8111/8168/8211/8411 PCI Express Gigabit Ethernet Controller) on my TUF GAMING X570-PLUS motherboard, running Fedora 40.

Overnight, the connection dropped from 1Gbps to 100Mbps.

When I manually configure the card to use a 1 Gbps connection, it becomes unstable and stops working correctly. However, the connection works fine at 100 Mbps.
Here’s what I’ve tried so far:

I’ve manually tried to force the connection to 1 Gbps using ethtool:

sudo ethtool -s enp5s0 speed 1000 duplex full autoneg off

After running this command, one of two things happens: either the issue persists, or it works temporarily.

Output of lspci -nnk:

05:00.0 Ethernet controller [0200]: Realtek Semiconductor Co., Ltd. RTL8111/8168/8211/8411    PCI Express Gigabit Ethernet Controller [10ec:8168] (rev 26)
      Subsystem: ASUSTeK Computer Inc. Device [1043:87c3]
      Kernel driver in use: r8169
      Kernel modules: r8169

My setup:

Fedora 40
Kernel: 6.11.3-200.fc40.x86_64
Motherboard: ASUS TUF GAMING X570-PLUS
Driver in use: r8169

What I’m looking for:

A solution to get my network card working stably at 1 Gbps.
Suggestions on proper configuration with ethtool or any other tools for managing high-speed networks.
If this is related to Fedora 40 or the kernel version I’m using, any suggestions for more stable drivers.

Thanks in advance for your help!

2

Check what your switch/router is doing as the speed is negociated bwtween the two of them.

It is worth change the ethernet cable and also using a different port on the switch to see if that changes things.

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3

It might possibly be a problem with the cable, as the higher speed needs a better quality cable.

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4

Thank you for your responses.
I indeed checked the router and noticed that the port was orange,
indicating a 100 Mbps connection.
Actually, I have two Ethernet sockets in my office. I switched to the other socket, and the connection returned to 1 Gbps.
I believe the wiring on the first socket is faulty.

Thank you again for your help, my issue is resolved.

5

The speed is normally autonegotiated as already mentioned.
Sometimes the port on the router may have an issue or the cable may be faulty and when that happens it often either falls back to the lower speed or fails completely.

In the past it often was necessary to set one end of the connection at a fixed speed so the autonegotiate was negated and the connection then would connect as expected. You have already tried that on your pc so it appears either the cable or the router port is the issue.

You can verify if it is the cable or port by swapping cables between the router ports.