Hello everyone.

I'm getting a hard time with Qualcomm Atheros AR8151 onboard LAN with Debian. It usually drops to 100Mb/s and freezes the network altogether

Settings for enp1s0:
Supported ports: [ TP ]
Supported link modes: 10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
1000baseT/Full
Supported pause frame use: No
Supports auto-negotiation: Yes
Supported FEC modes: Not reported
Advertised link modes: Not reported
Advertised pause frame use: No
Advertised auto-negotiation: Yes
Advertised FEC modes: Not reported
Speed: 100Mb/s
Duplex: Full
Auto-negotiation: on
Port: Twisted Pair
PHYAD: 0
Transceiver: internal
MDI-X: Unknown
Supports Wake-on: pg
Wake-on: d
Current message level: 0x0000003f (63)
drv probe link timer ifdown ifup
Link detected: yes
[ 3.004591] atl1c 0000:01:00.0 enp1s0: renamed from eth0

[ 37.754972] atl1c 0000:01:00.0: atl1c: enp1s0 NIC Link is Up<100 Mbps Full Duplex>

[ 45.071291] atl1c 0000:01:00.0: atl1c: enp1s0 NIC Link is Up<100 Mbps Full Duplex>
[ 45.799689] atl1c 0000:01:00.0: atl1c: enp1s0 NIC Link is Up<100 Mbps Full Duplex>

any tips of what can be done around here? I'm using kernel 6.12.111+deb13-amd64

Dumb question, but have you ruled out the cable being bad or corrosion in the socket? Dropping to 100 is usually something bad with the cable.

Does it persist if you change the cable, the device on the far side, the OS? What's in the log when it drops?

What are you plugged into?

I admit that at this very moment its running on a generic switch. I tried other cables, but no change.

no tdumb at all. I tried other cables, but I never got a fully cleanup on the socket itself. As it was an auction purchase, I guess some drops of deoxit and a good scrub won't make things any worse. Thanks!

That may be your problem. Do you have multiple 10G cards? Try doing a direct link between two machines. Auto MDIX will take care of the electrical connection but you will need to set static IPs in order to run a iperf3 test

Additionally, make sure you are using cat6/6a cables

If it's on a card, ditch it and replace it with a better one. If not, and you've got a spare slot, buy a new card.

Seen similar behaviour on Fedora and MXLinux. It was a kernel issue. Upgrading kernel solved it for me.