WifiOnICE @ DB with Linux and my Lenovo X260

I’m writing this while travelling with Deutsche Bahn to Munich, when I was haunted by longly forgotten memories of manual WiFi configurations and tweaking sessions: I had a hard time connecting my Lenovo X260 (with Fedora Linux) to the ICE’s on-board WiFi network.

First problem: deauthentications

First I realized that the my notebook was reconnecting all the time. Digging into syslog (dmesg -w), I saw lots of PREV_AUTH_NOT_VALID messges showing up:

[  729.081994] wlp4s0: deauthenticated from dc:77:4c:3f:7d:70 (Reason: 2=PREV_AUTH_NOT_VALID)

Doing a quick search on the internet, I found out that this seems to be a driver issue in the intel wifi driver. Setting the 11n_disable option of the iwlwifi driver fixed the problem for me. Create a file /etc/modprobe.d/iwlwifi.conf with the following contents

options iwlwifi 11n_disable=1

and restart the driver afterwards with sudo rmmod iwlmvm && sudo insmod iwlwifi. After that, the deauthentication problems were gone. But I still had no network access…

Second problem: docker IP address collision

After the driver problem was solved and I got a connection and an IP address, I I recognized that my docker network configuration collides with the IP range of the DB WLAN in the ICE. Both used IP addresses in the 172.18.0.0/16 range. That can be changed by modifiying /etc/docker/daemon.json to something like:

{
	"default-address-pools": [
		{"base": "10.10.0.0/16", "size": 24}
	]
}

That instructs docker to use IP addresses from the given 10.10.0.0/16 range. After that, make sure that you restart the docker daemon and optionally discard any existing docker networks with e.g.:

$ docker network list
$ docker network prune

Check the docker networks with docker network inspect to make sure there are no 172.18.0.0/16 addresses being used anymore.

Finally we have a running WiFi connection.

For today, I will not do further research on performance implications the iwlwifi setting has, or what the root cause of the problem is (bugs, incompatibilities or a deauther?), because fixing the problem already took most of my travel time. Tested with Fedora 38, Kernels 6.2 and 6.3.