Continuing my Bookmarks serie, here is how to tell NetworkManager to not manage an interface, thank you very much:

~# sudo cat >> /etc/NetworkManager/NetworkManager.conf << EOF
plugins+=keyfile
[keyfile]
unmanaged-devices=interface-name:IFNAME
EOF

Where IFNAME is the interface name. For example:

unmanaged-devices=interface-name:eth0

Will prevent NetworkManager to manage eth0. You can also specify interfaces using mac addresses with prefix mac::

unmanaged-devices=mac:ca:fe:de:ad:be:ef

Finally you can specify multiple devices, mixing both formats using ; to separate entries:

unmanaged-devices=mac:ca:fe:de:ad:be:ef;interface-name:eth0

Of course everything and more can be read in NetworkManager.conf(5).