Linux - Debian 12 Network Settings

How-To: Linux Networking

Photo by Lukas on Unsplash

Monday 20th October 2025

Disable Network Manager and enable ifupdown

If Debian was installed with a graphical interface, Network Manager is usually enabled. That is not ideal if you are using it as a server.

If you have Network manager active, this is how to disable it and rely on ifupdown instead:

Disable Network Manager

sudo systemctl stop NetworkManager 
sudo systemctl disable NetworkManager

Enable ifupdown

ifupdown (systemctl status networking) should be activated by default. If not, here is how to activate it:

sudo systemctl start networking
sudo systemctl enable networking

Then you just have to edit the /etc/network/interface file with your desired settings. Example:

auto ens19
iface ens19 inet6 static
  address 2001:db8:1234:10::1101/64
  gateway 2001:db8:1234:10::1

iface ens19 inet6 static
  address fe80::1101:1/64

iface ens19 inet static
  address 10.1.254.11/24
  gateway 10.1.254.1

Then restart the networking service and verify:

$ sudo systemctl restart networking
$ ip address show ens19
3: ens19: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 9198 qdisc fq_codel state UP group default qlen 1000
    link/ether bc:24:11:9b:db:c7 brd ff:ff:ff:ff:ff:ff
    altname enp0s19
    inet 10.1.254.11/24 brd 10.1.254.255 scope global ens19
       valid_lft forever preferred_lft forever
    inet6 2001:db8:1234:10::1101/64 scope global 
       valid_lft forever preferred_lft forever
    inet6 fe80::1101:1/64 scope link 
       valid_lft forever preferred_lft forever

Note: To create VRF and OOBM interfaces, read this post:
https://opensourceisfun.substack.com/p/debian-12-creating-a-management-interface

Enable DNS

Interface-specific DNS

In Debian you can configure DNS either by specifying dns-nameservers under a specific interface…

$ sudo nano /etc/network/interface

auto ens19
iface ens19 inet6 static
  address 2001:db8:1234:10::1101/64
  gateway 2001:db8:1234:10::1
  dns-nameservers 2620:0:ccc::2 2620:0:ccd::2

Global DNS

… Or globally by modifying /etc/resolv.conf:

$ sudo nano /etc/resolv.conf

search int.libertassolutions.io
nameserver 2620:0:ccc::2
nameserver 2620:0:ccd::2

Verify:

$ nslookup example.com
Server:         2620:0:ccc::2
Address:        2620:0:ccc::2#53

Non-authoritative answer:
...

Appendix

Install the ifconfig utility

There is nothing wrong with using the built in “ip address” commands that’s part of the iproute2 package. In fact that is the more maintaned version and is recommended for configuration.

For verifying configuraiton on links though, I think the output of “ifconfig” is better formatted. However, that tool is not included in Debian 12 but can be installed:

$ sudo apt install net-tools

Even after you install it, “ifconfig” won’t be recognized, unless you do “sudo ifconfig”. The reason for that is because /sbin is not included in the PATH variable for regular users and therefore needs to be added:

echo 'export PATH="$PATH:/sbin"' >> ~/.profile

Then logout and log back in again:

$ ifconfig ens19
ens19: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 9198
        inet 10.1.254.11  netmask 255.255.255.0  broadcast 10.1.254.255
        inet6 fe80::1101:1  prefixlen 64  scopeid 0x20<link>
        inet6 fe80::be24:11ff:fe9b:dbc7  prefixlen 64  scopeid 0x20<link>
        inet6 2001:db8:1234:10::1101  prefixlen 64  scopeid 0x0<global>
        ether bc:24:11:9b:db:c7  txqueuelen 1000  (Ethernet)
        RX packets 377  bytes 17526 (17.1 KiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 82  bytes 8725 (8.5 KiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0