On Fri, Jul 05, 2024 at 21:51:09 -0700, David Christensen wrote:
> What I really need is a good book or document that explains the design and
> implementation of networking with systemd and Network Manager on modern
> Debian GNU/Linux systems. Recommendations?
The main thing to understand is that there IS NOT a single unified
way of doing network configuration in Debian. Instead, there are
many choices.
So, the first thing you have to discover on your system is which
choices are in play. Once you know which things to investigate and
poke, then you can learn how those particular things work, by reading
the documentation that's specific to those things.
So, let's start at the interface level. Interfaces are named by the
kernel, when you boot. The kernel performs hardware probes, to discover
the network interfaces, both ethernet and wireless. The kernel
assigns TEMPORARY NAMES to each interface it finds, in the order in
which its probes happen to find them. These temporary names look like
"eth0", "eth1" and so on for ethernet interfaces, and "wlan0", "wlan1"
and so on for wireless.
If you've told your kernel NOT to perform the second step, then these
semi-randomly assigned temporary names become the permanent names of
your interfaces. Otherwise, the kernel performs some gymnastics to
try to assign "predictable" names to each interface. An onboard
ethernet interface, for example, may be renamed to "eno1", or a PCI
ethernet interface may be renamed to something like "enp2s0" based
on the PCI slot.
Or, if you don't want the kernel to assign names, you may choose your
own names for your interfaces, by configuring systemd.link(5) files.
To learn what your interface names are, you can start with this
command:
ip link
>From the output of that, you can deduce which naming scheme is being
used. You should be able to figure out which interfaces are ethernet
and which are wireless (hint: look at the first letter), and you might
be able to guess whether the names will remain stable over time, or
whether you should do something to switch naming schemes.
Once you have your interface names, there are three basic ways to
configure them:
1) /etc/network/interfaces a.k.a. /e/n/i a.k.a. ifupdown
2) NetworkManager
3) systemd.network(5)
Option 1 is the way Debian has always supported, for three decades.
See interfaces(5) for documentation of the main configuration file.
Option 2 is often installed by default if you install a Desktop
Environment package. In Debian, /e/n/i and NM will work together --
if an interface is configured in /e/n/i, NM will leave that interface
alone. There are three different ways to interact with NM -- a
set of command line tools (nmcli), a terminal-based interface (nmtui),
and a graphical interface (click things provided by your DE).
Option 3 is obviously part of systemd, and is not used in a default
Debian installation. However, you're free to use it if you wish.
Or, if someone else installed Debian for you, such as a VPS provider,
it's *possible* that they used this. Therefore, it's good to be
aware that it exists, and *might* be in play on your system, if you
weren't the one who installed Debian.
Once you figure out which option is being used, you can read the
documentation. I've provided man page references for the ones that
have them, and I've done my best to supply what little information I
have about NM.
