Kernel 6.18.20-1 breaks networking

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Kernel 6.18.20-1 breaks networking

Postby df8oe » Thu Mar 26, 2026 11:55 am

Hi to all,

using the mentioned kernel leads to network is broken. LAN (managed by NetworkManager) does not get IP via DHCP and all virtual network devices used by docker also are unmanaged. Downgrading kernbel to 6.18.18-3 solves the issue. I am using aarch64-architecture. Is it a bug or have I missed anything important?
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Re: Kernel 6.18.20-1 breaks networking

Postby graysky » Thu Mar 26, 2026 1:09 pm

No breakage here using systemd-networkd. Without more to go on, systemd status of MN service or journactl output for example, we are just guessing.
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Re: Kernel 6.18.20-1 breaks networking

Postby baslking » Thu Mar 26, 2026 2:11 pm

I too am running 6.18.20-1 with systemd-networkd like graysky with dhcp and a docker container with explicit port mappings, and I saw no issues. Not much help, but just another data point
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Re: Kernel 6.18.20-1 breaks networking

Postby Rapty » Sat Mar 28, 2026 10:59 am

Headless rpi4 here.
I can confirm network falls after boot with linux-rpi-6.18.20-1.
Network is okay at boot and then after a few minutes it collapses.
Had to revert to linux-rpi-6.18.18-3.

journalctl -u systemd-networkd doesn't show any difference between the two kernels' behavior.

Would be happy to share logs if you can point me which one you are looking for.
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Re: Kernel 6.18.20-1 breaks networking

Postby graysky » Sat Mar 28, 2026 3:11 pm

I have a 4B running linux-rpi 6.18.20-1. How do I trigger the NIC drop? My network.conf

[Match]
Name=e*

[Network]
DHCP=ipv4
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Re: Kernel 6.18.20-1 breaks networking

Postby Rapty » Sun Mar 29, 2026 10:24 am

Well, if I knew...
I don't have a network.conf but I have

[code]
$ cat /etc/systemd/network/en.network
[Match]
Name=en*

[Network]
Address=[ip6]
Address=[ip4]
Gateway=[gateway ip]
DNS=[dns one]
DHCP=no
DNSSEC=yes
[/code]
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Re: Kernel 6.18.20-1 breaks networking

Postby graysky » Sun Mar 29, 2026 8:51 pm

try my config?
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Re: Kernel 6.18.20-1 breaks networking

Postby technosf » Mon Mar 30, 2026 12:13 am

I had something similar on my MochaBin - network activity at boot and then someways into the boot all the network lights go off.

I found that as the boot progressed and settings were applied by systemd-networkd that one would apparently tripped the network and all the device leds would go dark. I would rollback, confirm that it was the change and review and retry.

I started with a bare minimum setup, versioned anything that worked and changed one thing at a time. Quite a learning experience, but now I run a static IPv6 and /56 block for my private network.
[size=85] MochaBin 5G || NSA325 [/size]
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Re: Kernel 6.18.20-1 breaks networking

Postby Rapty » Tue Mar 31, 2026 5:23 pm

[quote]
try my config?
[/quote]

Nothing change:
Boot fine, network is ok and after one or two minutes: network fails.

Nothing particular in journalctl.
Restarting systemd-netword doesn't put back network on track.
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Re: Kernel 6.18.20-1 breaks networking

Postby df8oe » Wed Apr 01, 2026 6:59 am

Same behaviour here using NetworkManager instead of systemd-networkd. Nothing in logs to identify the cause. I have reverted kernel and wait for next kernel release. Possible bug fixing I hope...

My /etc/NetworkManager/systemconnections/eth0.nmconnection:
[code][connection]
id=Supervisor eth0
uuid=something-here
type=ethernet
llmnr=2
mdns=2
timestamp=1774604758

[ethernet]
cloned-mac-address=preserve
mac-address=xx:xx:xx:xx:xx:xx

[match]
path=platform-fd580000.ethernet;

[ipv4]
method=auto

[ipv6]
addr-gen-mode=default
method=auto

[proxy]
[/code]
Of course I have
[code]net.ifnames=0[/code]
in cmdline.txt...
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