Shane Rainville
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How to configure network settings in Debian

Overview

In this tutorial, you will learn how to configure network in Debian to use static IP addresses and DHCP. You will also learn how to configure the DNS name servers, Gateways, and subnets.

This tutorial covers the following versions of Debian:

  • Debian 8 Jessie
  • Debian 9 Stretch
  • Debian 10 Buster

Network Interfaces Files

Debian’s network interfaces can be configured in two places. The primary location for network configurations is in the /etc/networks/interfaces file.

The second location for network configurations is under /etc/networks/interfaces.d, where you can drop network config files rather than storing everything in the interfaces file.

The /etc/networks/interfaces file looks like the following.

# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).

source /etc/network/interfaces.d/*

# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
allow-hotplug enp0s3
iface enp0s3 inet dhcp

The first thing the interfaces file does it load additional configuration files from /etc/network/interfaces.d, if any files are stored there. It then proceeds to load network configurations from defined below that line.

Setting a Static IP address

To set a static IP address for an interface named enp0s3, you would write the following configuration.

iface enp0s3 inet static
     address 192.168.1.2/24
     gateway 192.157.1.1

The configuration above does the following:

  • static sets the interface as static
  • address sets the IP address to 192.168.1.2 and its subnet using CIDR /24, or subnet 255.255.255.0.
  • gateway sets the network gateway IP address for routing traffic outside of the interface’s subnet.

This configuration can be added to the interfaces file or written to a configuration file under /etc/network/interfaces.d.

For example, the file could be saved as /etc/network/interfaces.d/enp0s3.conf.

To apply your new network settings you will need to bring the interface down and then back up again.

  1. Bring the interface you just updated down.
    ifdown enp0s3
  2. Bring the interface back online.
    ifup enp0s3

Verify your network settings are applied correctly. For Debian 10 and Debian 9, you can use the ip a command. For Debian 8 you would use the ifconfig command.

Setting a DHCP Address

A DHCP address is configured as shown in the example below. Unlike the the static IP address it’s a one-liner, as we do not need to set an address or gateway. These values will automatically be assigned by your network.

iface enp0s3 inet dhcp

Applying New Network Settings

To apply your new network settings you will need to bring the interface offline and then back online.

  1. Bring the interface down.
    ifdown enp0s3
  2. Bring the interface back online
    ifup enp0s3

Verifying network settings in Debian 9 and Debian 10

With Debian 9 and Debian 10 you must use the ip command to view the current state of your network interfaces. 

ip a
2: enp0s3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether 08:00:27:de:14:99 brd ff:ff:ff:ff:ff:ff
    inet 10.0.0.41/24 brd 10.0.0.255 scope global dynamic enp0s3
       valid_lft 562759sec preferred_lft 562759sec
    inet6 2607:fea8:4de0:b900:a00:27ff:fede:1499/64 scope global dynamic mngtmpaddr 
       valid_lft 298sec preferred_lft 298sec
    inet6 fe80::a00:27ff:fede:1499/64 scope link 
       valid_lft forever preferred_lft forever

In the output of the ip a command we can see that our interface, enp0s3, is in an UP state, has been assigned IP address 10.0.0.41/24. If you set your IP address to 10.0.0.41/24, then your changes have been applied successfully.

Verifying network settings in Debian 8

Network interfaces states can be check in Debian 8 using the ifconfig command.

ifconfig
lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:8 errors:0 dropped:0 overruns:0 frame:0
          TX packets:8 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:480 (480.0 b)  TX bytes:480 (480.0 b)

p2p1      Link encap:Ethernet  HWaddr 00:1C:C0:AE:B5:E6  
          inet addr:192.168.0.1  Bcast:192.168.0.255  Mask:255.255.255.0
          inet6 addr: fe80::21c:c0ff:feae:b5e6/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:41620 errors:0 dropped:0 overruns:0 frame:0
          TX packets:40231 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:21601203 (20.6 MiB)  TX bytes:6145876 (5.8 MiB)
          Interrupt:21 Base address:0xe000

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