Network/Ethernet limited to 100Mbps half duplex on startup.

[NertSkull]

When I boot and run this command I get the following:



$ ethtool eth0

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: No
Advertised FEC modes: Not reported
Speed: 100Mb/s
Duplex: Half
Port: Twisted Pair
PHYAD: 1
Transceiver: internal
Auto-negotiation: off
MDI-X: off (auto)
Cannot get wake-on-lan settings: Operation not permitted
Current message level: 0x00000007 (7)
drv probe link
Link detected: yes



And if I run a speed test, I get capped around 30 Mbps. My internet speed from my ISP is 100Mbps.

I dual boot, and in windows I immediately get 100Mbps.

If I run the following command


$ sudo ethtool -s eth0 speed 1000 duplex full

then I get my full 100mps download.

However, this command does not survive reboot.

This all started with a new router (Netgear R7800). On my old router, I never had these issues. I always got 100Mbps down on boot.

So a few questions.

1) Why would a new router change my computers default ethernet speed?
2) Is 'full duplex' what I want? It defaults now to half duplex, but that is legacy, right?
3) After running the above command, it now turns 'auto-negotiation' to 'on'. Is that better?

And most importantly

4) How do I fix this? Is the command above the correct thing to do? How do I make it survive reboot?


Info:
Kubuntu 18.04.2
Kernel 4.15.0-58-generic
ethernet connection (2) I219-v

[SeijiSensei]

Never seen this problem myself, but you can try


sudo echo 'ethtool -s eth0 speed 1000 duplex full' >> /etc/rc.local

Now reboot and see if that makes the fix permanent.

[NertSkull]

Yeah, I thought about doing something akin to that. It just seems really 'hacky' to me.

But if that's my only/best option I can do that. It just makes no sense to me that I changed literally nothing on my computer. I just installed a new router and things are now different. Same cables and everything.

I feel there has to be something more going on that has a 'real' fix.

[SeijiSensei]

Well, sure, but do you want to futz with your computer, or do you want to use it?

[NertSkull]

Seems to be my eternal debate while using ubuntu/linux.

I mean yeah I want to use it. But I always feel that when things aren't working 'the way they should' that I'm missing something else that is wrong and that I would like fixed. Especially if it could in anyway affect security.

For now I'll probably us rc.local. But I'd still like to figure out what is going on if anyone has any bright ideas.

[him610]

NertSkull,
Your post got me to wondering about my own connection using ethtool which is shown below with differences highlighted -


Speed: 1000Mb/s
Duplex: Full
Port: Twisted Pair
PHYAD: 1
Transceiver: internal
Auto-negotiation: on
MDI-X: on (auto)

These get set during installation. Don't know how to effect a change in them. It may have something to do with the quality of your Cat5/Cat5e cable to your router.