Unfortunately, on Debian-based systems (Debian, Ubuntu, Raspberry Pi OS), there are various ways to configure the network of the system - depending on the distro:

• ifupdown
• systemd-networkd
• NetworkManager
• netplan

For each, this article shows how to:

• Assign IP address via DHCP (for IPv4)
• Assign static IP address (including DNS)
• Connect to WiFi

As a bonus, this article also shows how to get back the old eth0 etc. network device names.

$ which bash
/usr/bin/bash

$ which i-do-not-exist  # no output

Basics #

Show network interfaces #

To list all network interfaces, call:

ip a

Each interface will be listed with a status of UP (works) or DOWN (doesn’t work).

DNS #

Most base/traditional software on Debian uses /etc/resolv.conf to determine the DNS server(s) and DNS-related settings. More modern software may decide to ignore this file and use systemd-resolved directly - but will fall back to resolv.conf if no other DNS resolver is available.

Normally, this file is automatically managed by the DNS software on the system (like resolvconf, dhcpcd, systemd-resolved, …). The DNS software either writes directly to this file, or creates a symlink to another file (ls -l /etc/resolv.conf).

However, in case something went wrong, you can manually edit this file:

nameserver 192.168.0.1

Alternatively, you can use a public DNS resolver like Cloudflare’s 1.1.1.1.

Wi-Fi #

Wi-Fi network devices show up as wl... or wlanX in ip a.

If that’s the case, your Wi-Fi device is ready to be used.

If it doesn’t show up, you may need to install additional firmware like firmware-realtek and then reboot.

ifupdown #

ifupdown is the oldest and most basic network configuration system. However, it’s still used as default in Debian 13 on minimal installs.

Is active: systemctl status networking

Packages: ifupdown, dhcpcd-base (DHCP), resolvconf (DNS), wpasupplicant (Wi-Fi)

Config files: /etc/network/interface or /etc/network/interfaces.d/*

Wi-Fi password stored in: /etc/wpa_supplicant/wpa_supplicant.conf

Reload network config: sudo ifdown ens18 && sudo ifup ens18

Wildcard support for interface names: no (each interface must be explicitly specified)

systemctl services: networking, wpa_supplicant (Wi-Fi)

DHCP #

In /etc/network/interface or /etc/network/interfaces.d/some-file:

allow-hotplug ens18
iface ens18 inet dhcp

This assigns an IPv4 address (inet) to the device ens18 via DHCP.

Static IP Address #

In /etc/network/interface or /etc/network/interfaces.d/some-file:

allow-hotplug ens18
iface ens18 inet static
    address 192.168.0.10
    netmask 255.255.255.0
    gateway 192.168.0.1
    dns-nameservers 192.168.0.1
    dns-search fritz.box  # optional

Side Note: auto vs allow-hotplug #

You can configure interfaces both with auto and with allow-hotplug:

auto ens18
iface ens18 inet dhcp

allow-hotplug ens19
iface ens19 inet dhcp

auto brings up the device at boot time. If the device is not available then, your boot process will hang.

allow-hotplug brings up the device when it becomes available (from man interfaces):

Interfaces marked “allow-hotplug” are brought up when udev detects them. This can either be during boot if the interface is already present, or at a later time, for example when plugging in a USB network card. Please note that this does not have anything to do with detecting a network cable being plugged in.

Of the two, allow-hotplug is recommended - unless you need network access very early during boot (for example, for nfs or smb mount in fstab without nofail).

Wi-Fi #

For Wi-Fi to work, you need the wpa_supplicant package:

apt install wpa_supplicant

Then you can create the Wi-Fi settings file (wpa_supplicant.conf) via:

wpa_passphrase "YOUR_SSID_HERE" > /etc/wpa_supplicant/wpa_supplicant.conf
chmod 0600 /etc/wpa_supplicant/wpa_supplicant.conf

This will read the Wi-Fi passphrase from the command line.

This file will look like:

network={
    ssid="YOUR_SSID_HERE"
    psk=4a3f2...
}

Next, you need to add the wpa-conf directive to your interface configuration:

allow-hotplug wlan0
iface wlan0 inet dhcp
    wpa-conf /etc/wpa_supplicant/wpa_supplicant.conf

It’s recommended to use allow-hotplug here (instead of auto) so that the boot process doesn’t hang if the wifi is not available.

If you get a timeout here:

• Check if the Wi-Fi network is hidden. In this case, add scan_ssid=1 to network={} block in wpa_supplicant.conf.
• Check if the Wi-Fi network has a MAC address filter enabled.

systemd #

systemd (or more specific: systemd-networkd) is modern replacement for ifupdown. Nowadays, systemd comes preinstalled on most Debian-based distros (including Ubuntu and Raspberry Pi OS).

Is active: systemctl status systemd-networkd

Packages: systemd, systemd-resolved (DNS), iwd or wpa_supplicant (Wi-Fi)

Config files: /etc/systemd/network/*

Wi-Fi password stored in: /var/lib/iwd/<SSID>.psk

Reload network config: sudo systemctl reload systemd-networkd

Wildcard support for interface names: yes (*, ?, and [...])

systemctl services: systemd-networkd, systemd-resolved (DNS), iwd or wpasupplicant (Wi-Fi)

DHCP #

/etc/systemd/network/ethernet.network:

[Match]
Name=ens18

[Network]
DHCP=yes

Static IP Address #

/etc/systemd/network/ethernet.network:

[Match]
Name=ens18

[Network]
# In CIDR notation; /24 is subnet mask 255.255.255.0
Address=192.168.0.10/24
Gateway=192.168.0.1
DNS=192.168.0.1
Domains=fritz.box

Wi-Fi #

systemd works both with wpa-supplicant (used by ifupdown above) or iwd (iNet wireless daemon). Of the two, iwd is recommended for use with systemd.

iwd (iNet wireless daemon) is a wireless daemon for Linux written by Intel. The core goal of the project is to optimize resource utilization by not depending on any external libraries and instead utilizing features provided by the Linux Kernel to the maximum extent possible. source: Arch Wiki

You first need to configure your network interface with systemd, e.g.:

/etc/systemd/network/wifi.network:

[Match]
Name=wlan0

[Network]
DHCP=yes

To connect the network interface to a Wi-Fi network (will ask for the Wi-Fi password):

iwctl station wlan0 connect "MySSID"

The settings are stored in: /var/lib/iwd/<SSID>.psk

See which Wi-Fi network an interface is connected to:

iwctl station wlan0 show

NetworkManager #

Like systemd, NetworkManager is a modern replacement for ifupdown. NetworkManager is more designed for desktop systems than servers (but still Raspberry Pi OS uses it by default). Unlike systemd, it comes with a UI (both GUI and TUI) to configure your network interfaces.

Is active: systemctl status NetworkManager

Packages: network-manager

Config files: /etc/NetworkManager/system-connections/*.nmconnection

Wi-Fi password stored in: /etc/NetworkManager/system-connections/<SSID>.nmconnection

Reload network config: nmcli connection reload

Wildcard support for interface names: Automatic DHCP for all managed interfaces

systemctl services: NetworkManager

Configuring Network Interfaces #

To configure network interfaces with NetworkManager:

nmtui

The related configuration files will be stored in /etc/NetworkManager/system-connections/*.nmconnection.

nmcli -f device,state,name,type,filename connection show

Managed Interfaces #

NetworkManager distinguishes between managed and unmanaged network interfaces. NetworkManager only manages “managed” interfaces and leaves unmanaged ones alone.

To see managed status:

nmcli device

Unmanaged interfaces are listed as “unmanaged”. All other interfaces are managed.

netplan #

netplan is Ubuntu’s solution to have a unified configuration language for both systemd and NetworkManager. Although it was designed for Ubuntu, it works on any Debian system. Unlike systemd and NetworkManager, netplan itself doesn’t do any network interface configuration. Instead, it creates configuration files for either systemd or NetworkManager.

Is active: which netplan

Packages: netplan.io

Config files: /etc/netplan/*.yaml (not .yml!) - documentation

Wi-Fi password stored in: /etc/netplan/*.yaml

Reload network config: netplan apply

Wildcard support for interface names: Yes, via match.name (documentation)

systemctl services: -

Renderers #

netplan has two renderers: systemd and NetworkManager.

The renderer determines which “backend” is used by netplan.

To use systemd:

network:
  renderer: systemd  # the default; can also be omitted

To use NetworkManager:

network:
  renderer: NetworkManager

DHCP #

/etc/netplan/my-connection.yaml:

network:
  #renderer: NetworkManager
  ethernets:
    eth0:
      dhcp4: true

Static IP Address #

/etc/netplan/my-connection.yaml:

network:
  #renderer: NetworkManager
  ethernets:
    eth0:
      addresses:
        - 192.168.1.194/21
      routes:  # default gateway
        - to: default
          via: 192.168.0.1
      nameservers:  # DNS settings
        search: [fritz.box]
        addresses: [192.168.0.1]

Wi-Fi #

/etc/netplan/my-connection.yaml:

network:
  #renderer: NetworkManager
  wifis:
    wlan0:
      access-points:
        "My-SSID":
          password: 'my-wifi-password'
      #dhcp4: true
      addresses:
        - 192.168.1.196/21
      routes:
        - to: default
          via: 192.168.0.1
      nameservers:
        search: [fritz.box]
        addresses: [192.168.0.1]

Get eth0 back #

Linux introduced predictable network interface names (enp0s31f6) around 2015 and they became the default in around 2017. They were introduced because the traditional interface names (eth0, eth1, wlan0) would sometimes assigned to different network adapters after a reboot.

Of course, this could only happen for machines that have multiple network adapters. For machines with just one network adapter, the traditional interface names work fine and can actually be more stable (because changing the PCI slot can change the name of a “predictable network interface name”).

To get the traditional names back:

1. Edit GRUB defaults:

   
   nano /etc/default/grub
   

2. Find the line:

   
   GRUB_CMDLINE_LINUX=""
   

3. Change it to:

   
   GRUB_CMDLINE_LINUX="net.ifnames=0"
   

4. Update GRUB:

   
   update-grub
   

5. Reboot:

   
   reboot