Where are all the network-bridges coming from, ifconfig shows me?

I'm using Ubuntu 18.04.3 LTS

As I'm a developer, I have Docker, docker-compose and Virtualbox and Vagrant installed

If I enter in a terminal:

$ ifconfig

I got a long list of network bridges.

br-2fdf26d8ad11: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500 inet 192.168.240.1 netmask 255.255.240.0 broadcast 192.168.255.255
br-3097f1941dd7: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500 inet 192.168.32.1 netmask 255.255.240.0 broadcast 192.168.47.255
br-604e362c8abb: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500 inet 172.28.0.1 netmask 255.255.0.0 broadcast 172.28.255.255
br-6bec4010864a: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500 inet 172.23.0.1 netmask 255.255.0.0 broadcast 172.23.255.255
br-729cfdd5c2dd: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500 inet 192.168.48.1 netmask 255.255.240.0 broadcast 192.16628.63.255
br-72c49f160076: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500 inet 172.19.0.1 netmask 255.255.0.0 broadcast 172.19.255.255
br-765c8f8c1edf: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500 inet 172.18.0.1 netmask 255.255.0.0 broadcast 172.18.255.255
br-7b6ec7d56aec: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500 inet 172.31.0.1 netmask 255.255.0.0 broadcast 172.31.255.255
br-9392c09745cd: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500 inet 172.27.0.1 netmask 255.255.0.0 broadcast 172.27.255.255
br-97685d1968fe: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500 inet 172.26.0.1 netmask 255.255.0.0 broadcast 172.26.255.255
br-9b033123127c: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500 inet 172.17.0.1 netmask 255.255.0.0 broadcast 172.17.255.255
br-bc2ff863085c: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500 inet 192.168.96.1 netmask 255.255.240.0 broadcast 192.168.111.255
br-bcc4b1218247: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500 inet 172.30.0.1 netmask 255.255.0.0 broadcast 172.30.255.255
br-d7d1dd0718f3: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500 inet 192.168.80.1 netmask 255.255.240.0 broadcast 192.168.95.255
br-dd4949ff923c: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500 inet 172.25.0.1 netmask 255.255.0.0 broadcast 172.25.255.255
br-de108e80ee4d: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500 inet 172.21.0.1 netmask 255.255.0.0 broadcast 172.21.255.255
br-e37000236cd8: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500 inet 192.168.0.1 netmask 255.255.240.0 broadcast 192.168.15.255
br-ec26f968abd4: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500 inet 172.20.0.1 netmask 255.255.0.0 broadcast 172.20.255.255
br-fa80bcc7af95: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500 inet 172.24.0.1 netmask 255.255.0.0 broadcast 172.24.255.255
docker0: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500 inet 172.29.0.1 netmask 255.255.0.0 broadcast 172.29.255.255
enp0s31f6: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500 ether xx:xx:xx:xx:xx:xx txqueuelen 1000 (Ethernet)
lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536 inet 127.0.0.1 netmask 255.0.0.0 inet6 ::1 prefixlen 128 scopeid 0x10<host>
vboxnet0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500 inet 172.22.101.1 netmask 255.255.255.0 broadcast 172.22.101.255
wlp4s0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1492 inet 192.168.2.5 netmask 255.255.255.0 broadcast 192.168.2.255

I'm not sure, where they all come from.

My problem is, that, if I want to use a public network (train, airports and so on), they normally run on 172.xx -> normally it's already used by a bridge, so I first have to bring it down and then delete it, as described in my blog

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

I also read, that if you use the Ubuntu Network Manager, they can all come back.

I was trying to understand, where they come from but I haven't understood it yet really.

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