Score:1

Ubuntu

Preventing Network Interface from changing speed ubuntu server

Hans Yulian

2/21/24, 1:14 PM

Currently i'm stuck in trying to make my server a reliable router. It keep dropping the connection randomly. After checking and debugging for some time, i finally find out the problem.

The connection drop only happened when my interface, either it's the WAN or LAN interface changing speed from 100mbps to 1gbps and vice versa. I can test the ping when it change the speed, either by using ethtool or it's own, the ping resulted around 700ms from normally 0-1ms which is enough to drop connection in online gaming/video call.

So my question is, is there a way to either:

Force the speed into 1gbps, not allowing it to change at all
Force the speed on 100mbps, then i will just use the line as dedicated internet, and i will give another network card for my file server
Better solution to my problem?

I have tried many things, including ethtool, but no luck.

132

2 + 0

server

networking

22.04

Score:1

Ubuntu

Hans Yulian

2/25/24, 3:59 AM

So after several days digging, i finally found the issue. the issue wasn't:

bad cable
bad switch
bad NIC
or anything physical there

So actually, i'm using dnsmasq as the DNS and DHCP server for my home network. When you start dnsmasq, by default it will fail because the service of systemd-resolved is using same port 53 which is used by DNS. Many online guide on using dnsmasq is asking to just disable the systemd-resolved by using systemctl disable, but many source actually say that this service is very important for entire system and do it at your own risk.

So i decided to backup most of my home server settings, and then i reinstall the ubuntu and do some testing. In that testing on fresh system, i do find that the ethernet speed and negotiation are stable. So here my testing:

I tested that fresh system as only NAS for 1 day, without using it as DHCP and DNS server. PASS

I then reconfigure that system with dnsmasq but this time i dont disable systemd-resolved, but instead i follow the guide here: https://www.linuxuprising.com/2020/07/ubuntu-how-to-free-up-port-53-used-by.html.

vim /etc/systemd/resolved.conf
add DNSStubListener=no
reboot system

And viola! now my home server work perfectly even better than my router, using my old gaming pc:

Gigabyte X79 UD3
i7 3820
32GB Corsair Dominator 1600 C9
4x4 TB HDD in raid z1
1 NVMe for main purpose
64GB Sandisk USB 3.2 as boot
Realtek 8125 PCIe 2.5gbe 4 port

And there we go!

+ 0

Score:0

Ubuntu

Claus Holm Christensen

2/21/24, 2:35 PM

Speed changes usually indicate that the physical cable is bad, bent or otherwise broken. Please try another network cable first.

+ 7

Hans Yulian

2/21/24, 2:59 PM

it's same with other known good cables, at 1000mbps also it works just fine, it just that it sometimes change speed to 100mbps when not being used, but the moment it's used to the 1gbps, it spent 700ms to change to to 1gbps, same with changing back to 100mbps

Claus Holm Christensen

2/21/24, 4:10 PM

Trouble is, if you fix the speed, then the computer will just disconnect you instead of reducing speed. I'll assume that's worse.

Hans Yulian

2/21/24, 11:28 PM

Yes that happens too, but i notice that my windows machine always running on 1gbps all time with no issue, i can monitor this from my router. Cant ubuntu do the same?

Claus Holm Christensen

2/22/24, 8:26 AM

Yes, Ubuntu will also do the same, if in any way possible. Have you tried swapping the ends of the network cable (it forces you to disconnect and re-route the cable)?

Hans Yulian

2/22/24, 1:55 PM

yes, i even tried to change to the know good cable, no luck

Claus Holm Christensen

2/24/24, 11:34 AM

If the cable really is known good, then it must be something else. Did you try another outlet in the router? If not that, then look at the dmesg output for some details about the reasons for the speed change, but then I'm not really able to help you with the issue.

Hans Yulian

2/25/24, 3:51 AM

i found the issue, has been testing for 3 days and it's stable now, check my answer

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