Reconcile Docker with Deutsche Bahn.

content/posts/2024/reconcile-docker-with-deutsche-bahn/index.md

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+---
+title: "Reconcile Docker With Deutsche Bahn"
+description: >
+  If WiFi does not work on Deutsche Bahn's ICE trains and you have Docker installed,
+  there may be network interference which can be fixed easily.
+date: 2024-09-26T09:07:30Z
+draft: false
+# ShowLastmod: true
+toc: false
+scrolltotop: true
+#featuredImg: reconcile-docker-with-deutsche-bahn.png
+tags:
+  - network
+  - Deutsche Bahn
+  - Docker
+  - travel
+---
+
+![Composition of screenshots](reconcile-docker-with-deutsche-bahn.png)
+
+If you happen to be a (Linux) power user travelling on a Deutsche Bahn [ICE
+long-distance train][ice] and you wonder why you don't get a working network
+connection with the complimenatary "WIFIonICE" wireless network, there may be a
+network interference on your laptop.
+
+There are multiple solutions for this on the web. My favorite solution is to
+change Docker's network configuration by editing (or creating) the file
+`/etc/docker/daemons.json`. However, you may need to prune existing Docker
+networks first. Otherwise the Docker service will fail to start with the
+following message:
+
+```plain
+failed to start daemon: Error initializing network controller: error creating default "bridge" network: all predefined address pools have been fully subnetted
+```
+
+Therefore, I recommend the following steps (this is on a Fedora Linux system with *systemd*):
+
+1. Stop any docker containers that you may have running, including services managed by docker compose.
+2. Prune the networks:
+
+   ```bash
+   docker network prune
+   ```
+
+3. Create or edit `/etc/docker/daemon.json` so that it contains the following:
+
+   ```plain
+   {
+       "default-address-pools":
+       [
+           {"base":"172.19.0.0/16","size":24}
+       ]
+   }
+   ```
+
+4. Restart docker:
+
+   ```bash
+   systemctl restart docker
+   ```
+
+5. Connect to `WIFIonICE` and enjoy your network connection :-)
+
+## References
+
+- StackExchange answer that provides the solution as presented here -- see also
+  the answer about pruning the networks below.
+
+  <https://unix.stackexchange.com/a/539258/110635>
+
+- If you don't want to or cannot configure your Docker networks, you can also
+  turn Docker off and on again when you travel:
+
+  <https://kuttler.eu/code/ice-wlan-linux-docker/>
+
+  This is what I used to do myself, but nowadays I prefer to just configure the
+  Docker network differently.
+
+- There are many more internet sources (and I have just added another one...), I
+  won't copy all those links into my post, see DuckDuckGo search results
+  for yourself:
+
+  <https://duckduckgo.com/?q=docker+wifi+on+ice>
+
+[ice]: https://int.bahn.de/en/trains/long-distance-trains