mjhjmtu

What is the naming convention standard for Ethernet and Wi-Fi interfaces on a Linux machine?

We are developing a tool that should show only the Ethernet and Wi-Fi interfaces of the Linux machine and its current status.

For example, below are the list of network interfaces (both physical and virtual) on my Linux (Ubuntu) machine.

docker0, enp0s25, lo, wlp3s0

When I run the tool, below is the result I will be getting.

enp0s25, wlp3s0

We have written the code with the logic that all the Ethernet interfaces always start with word e and Wi-Fi interfaces always start with word w.

Is the logic right? If not, how can we address this?

Network interfaces can be named anything, so no matter what you do, you'll run into situations where (1) there is a "physical" network interface with a name that didn't match your pattern, or (2) there is a "physical" network interface that will match your pattern.

On top of that, if I was a user of your tool, the moment your tool wouldn't allow me to do something I want, because I have a network interface which is "virtual", though for practical purposes it should be considered "physical" in my setup, I'd start cursing loudly and forcefully at your app, and won't ever use it again.

Physical and virtual network interfaces all share a common API are one thing which makes Linux really flexible. Please don't try to babysit your user, and take that away from him or her. Your users will thank you.

For systemd predictable interface names, the prefixes can be seen in udev-builtin-net_id.c :

* Two character prefixes based on the type of interface:
* en — Ethernet
* ib — InfiniBand
* sl — serial line IP (slip)
* wl — wlan
* ww — wwan

so for both the traditional ethX style of naming and the newer systemd naming, an initial letter e should be an ethernet interface for any automatically generated interface names. All wifi interfaces should begin with a w in both schemes, although not all interfaces beginning with w will be wifi.

If this tool has to work in an arbitrary environment (rather than just on internal environments which you control), note that users may rename interfaces on linux systems with arbitrary names, such as [wan0, lan0, lan1, dmz0] which will break any assumptions about initial letters.

The naming convention is that LAN interfaces are named eth0, eth1, ... and that WLAN interfaces are named wlan0, wlan1, ...

What you see are the so called "predictable names" that systemd introduced. In practice, they are anything but predictable, and they can even change when the hardware is changed, which is exactly the problem they are supposed to avoid.

For a guess the start letter may be good enough. Some interfaces, in particular WLAN, have hints in /sys/class/net/*/uevent:

DEVTYPE=wlan

Unfortunately, there is no such DEVTYPE for LAN interfaces.

One caveat with my answer (applies to most of the others, too): I don't know the purpose of your application. If it is a throwaway application to troubleshoot one particular problem, or to understand networking better, never to be used again, then relying on the first letter of the interface may be a great quick-and-dirty option. If you are planning to write the next competitor to Wireshark or tcpdump, you need to be sure you get it right for all kinds of edge cases.

And if the application you are writing falls somewhere between those extremes, only you (and your customers) can know how carefully you need to implement your logic.

Others have already pointed out that the names are never reliable, for any number of reasons. The ultimate problem is a very common one in software: hard-coding assumptions instead of relying on known/documented facts.

The second issue that hasn't been mentioned is also based on an assumption about your requirements: that the list of interfaces you want to list is always exactly "hardware ethernet interfaces" and "wifi interfaces".

The third issue is yet another assumption: that all interface will fall into the categories you can think of right now. How about Infiniband, as mentioned by @user4556274? How about tunnel interfaces for a VPN? How about bridged interfaces? How about bridged interfaces that combine physical and logical interfaces?

But there may be options to accomplish what you are looking for. First, define exactly what characterizes an interface you want to list, vs one that you don't.

In most cases, one characteristic you can rely on is the routing table (however, this will only work as long as the interface is up, so it may not be what you are actually looking for).

Any interface that has a default route (i.e., a route to 0.0.0.0) is likely to be one you are looking for.

Note that even this is still based on an assumption, just a more reliable one: it is conceivable that a system is configured to route all outbound traffic through a virtual machine or a docker container (for instance, if there is a container running a firewall). And the reverse is also true: a sysadmin could potentially lock down outside traffic by deleting the default route.

Another option is to go by the actual hardware and see which driver it uses. You can then exclude certain well-known drivers

Are you explicitly excluding bonded or teamed interfaces? Our default here is to use bond0 or team0 for the primary interface for our servers.

I think you need to re-think your logic. Maybe try iterating though all the defined network interfaces on a given system, divide them up between ethernet, wifi, infiband, serial, etc., and then do your magic.