Context for newbies: Linux refers to network adapters (wifi cards, ethernet cards, etc.) by so called “interfaces”. For the longest time, the interface names were assigned based on the type of device and the order in which the system discovered it. So, eth0, eth1, wlan0, and wwan0 are all possible interface names. This, however, can be an issue: “the order in which the system discovered it” is not deterministic, which means hardware can switch interface names across reboots. This can be a real issue for things like servers that rely on interface names staying the same.
The solution to this issue is to assign custom names based on MAC address. The MAC address is hardcoded into the network adaptor, and will not change. (There are other ways to do this as well, such as setting udev rules).
Redhat, however, found this solution too simple and instead devised their own scheme for assigning network interface names. It fails at solving the problem it was created to solve while making it much harder to type and remember interface names.
To disable predictable interface naming and switch back to the old scheme, add net.ifnames=0 and biosdevname=0 to your boot paramets.
The template for this meme is called “stop doing math”.
I always just derive the interface name from first principles. Like, if I want to know which interface will be used to get out to the internet in a script, I’ll just find the one that’s L2 adjacent with the default gateway. If I’m given an egress or cidr, I’ll just find the interface that has that IP. Modern
iproute2has a JSON output option which makes getting this information pretty trivial. Doing that means that it doesn’t matter what scheme your OS is using.I personally prefer the persistent names for Ethernet, although I don’t like them for WiFi. Luckily, it seems like my wireless adapter always just ends up as wlan0. I’m not sure why that’s the case, but it works out well in the end for me.