Ubuntu – docker0 network interface is screwing up the network

Probably, when pluging in the ethernet cable, your default route gateway changes by dhcp. You send packets from wlan0 but your system doesn't know who is the gateway to forward them to. This way you can only ping systems within 192.168.1 network but not further. If you want to get a reply from the google server, you'll have to either change the default gateway back to the wireless router, or add a specific route for this server.

route add -host 74.125.230.112/32 gw 192.168.1.1 # assuming 192.168.1.1 is the wireless router's ip

Surely this is a problem that cloud providers (Azure, AWS, RackSpace, Openstack) have already solved when they import vms.

I think OpenStack uses cloud-init, ConfigDrive format, and provides a network configuration that matches the VM hardware. Sources:

• https://bugs.launchpad.net/cloud-init/+bug/1577747
• https://cloudinit.readthedocs.io/en/latest/topics/datasources/configdrive.html?highlight=configdrive
• https://ask.openstack.org/en/question/63105/ways-to-inject-networking-configuration-on-instance-boot/
• https://access.redhat.com/documentation/en/red-hat-enterprise-linux-atomic-host/version-7/installation-and-configuration-guide/#setting_up_cloud_init

If you rule out a first-boot script, there is one obvious answer.

Previously it was practically guaranteed that hosts equipped with a single ethernet card only had a single "eth0" interface. With this new scheme in place, an administrator now has to check first what the local interface name is before he can invoke commands on it where previously he had a good chance that "eth0" was the right name.

I don't like this, how do I disable this?

You basically have three options:

1. You disable the assignment of fixed names, so that the unpredictable kernel names are used again. For this, simply mask udev's .link file for the default policy: ln -s /dev/null /etc/systemd/network/99-default.link

https://www.freedesktop.org/wiki/Software/systemd/PredictableNetworkInterfaceNames/

Switching back to the old persistent interface names is not one of the options documented.

The other alternative is a setup where network interfaces are enabled by default, regardless of their exact name. I think NetworkManager supports this by default. systemd-networkd can also be told to do this.

As soon as you have more than one network device for a VM, they probably need specific configuration anyway...

Outside of VM's, there is one obvious advantage of the NetworkManager-style approach: a PC might have multiple network interfaces, perhaps of different types, with only one of them being connected. For example this can be seen on some premium motherboards, or on a system where the first network interface did not work as desired and a second interface was installed at some point.