On Thu, Oct 28, 2021 at 09:34:26PM -0400, Paul M. Foster wrote: > Well, that's interesting. Here is my /etc/network/interfaces: > > === > > source /etc/network/interfaces.d/* > > > # The loopback network interface > > auto lo > > iface lo inet loopback > > === > > There's nothing in /etc/network/interfaces.d/ . This is a stock Debian 11 > install, so whatever's in this file hasn't been messed with. No mention of > eno1. However, it DOES come up. Any clues?
There's no such thing as a "stock install". There are many possible installs, depending on which choices you make during the installation. If your interface isn't defined in /e/n/i then the most likely place it's being brought up is in Network-Manager. If it's not N-M then perhaps someone has configured your system to use systemd-networkd, but that's not enabled by default in Debian, so it's far less common.
