Deutsche Bahn,Docker and Wifi in an ICE and VPN problems

The Deutsche Bahn is providing free wifi for some years now. It works for most of the people pretty well, but if you are a developer you could have some issues. I was suffering a lot with this, this is why I’m posting it, to help some of you

As you can see, the WiFi is running on the IP 172.18.xxx

wp_wifi_on_ice

If you are running docker it can happen, that you have in your ifconfig a bridge already on this IP:

$ ifconig

br-bcc4b1218247: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500
inet 172.18.0.1 netmask 255.255.0.0 broadcast 172.30.255.255
ether 02:42:55:fb:67:74 txqueuelen 0 (Ethernet)
RX packets 0 bytes 0 (0.0 B)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 0 bytes 0 (0.0 B)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

you can delete this bridge by using the following commands:

sudo ip link set br-bcc4b1218247 down
sudo brctl delbr br-bcc4b1218247

This should work, that you can connect then to the WiFi on Ice

I had the problem, that I could not reach some websitse in our company network,when I’m using a VPN. The ping to our internal subdomain was working, but I could not reach it in my browser:

$ ping subdomain.intern.ourdomain.net
PING something.elb.amazonaws.com (10.x.x.x) 56(84) bytes of data.
64 bytes from 10.x.x.x (10.x.x.x): icmp_seq=1 ttl=254 time=108 ms
64 bytes from 10.x.x.x (10.x.x.x): icmp_seq=2 ttl=254 time=192 ms
64 bytes from 10.x.x.x (10.x.x.x): icmp_seq=3 ttl=254 time=697 ms
64 bytes from 10.x.x.x (10.x.x.x): icmp_seq=4 ttl=254 time=344 ms
64 bytes from 10.x.x.x (10.x.x.x): icmp_seq=5 ttl=254 time=52.2 ms
64 bytes from 10.x.x.x (10.x.x.x): icmp_seq=6 ttl=254 time=54.3 ms
64 bytes from 10.x.x.x (10.x.x.x): icmp_seq=7 ttl=254 time=267 ms
64 bytes from 10.x.x.x (10.x.x.x): icmp_seq=8 ttl=254 time=181 ms
64 bytes from 10.x.x.x (10.x.x.x): icmp_seq=9 ttl=254 time=141 ms
--- something.elb.amazonaws.com ping statistics ---
9 packets transmitted, 9 received, 0% packet loss, time 13011ms

the ifconfig for the vpn tunnel and the wifi were showing the following:

....
tun0: flags=4305<UP,POINTOPOINT,RUNNING,NOARP,MULTICAST> mtu 1500
....
wlp4s0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1440
.....

My colleague, who is traveling every day by the ICE of Deutsche Bahn told me to set down the MTU, then everything was working: