How to create a virtual network interface in Ubuntu 20.04

Introduction

A virtual interface is a networking interface, that mimics a physical interface. With the help of virtual interfaces creating virtual machines or containers are possible.

Adding virtual interface.

Adding a virtual interface is a very simple and straight task. This can be done with ip command and with some arguments.

In the below-mentioned command, I have added an interface with the name vr-br.

Adding a non persistent interface

Use the following command to add a nonpersistent interface. In the following command dummy is the kernel module.

sudo ip link add name <virtual_interface_name> type dummy

Example of the above command and its verification is shown in the following code section

ubuntu@ubuntu-exp:~$ sudo ip link add name vr-br type dummy
ubuntu@ubuntu-exp:~$ 
ubuntu@ubuntu-exp:~$ 
ubuntu@ubuntu-exp:~$ ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: ens3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1450 qdisc fq_codel state UP group default qlen 1000
    link/ether fa:16:3e:6e:46:61 brd ff:ff:ff:ff:ff:ff
    inet 10.0.1.62/8 brd 10.255.255.255 scope global dynamic ens3
       valid_lft 77157sec preferred_lft 77157sec
    inet6 fe80::f816:3eff:fe6e:4661/64 scope link 
       valid_lft forever preferred_lft forever
3: vr-br: <BROADCAST,NOARP> mtu 1500 qdisc noop state DOWN group default qlen 1000
    link/ether 3a:4f:ec:a3:ad:68 brd ff:ff:ff:ff:ff:ff
ubuntu@ubuntu-exp:~$ 

You can then play with the interface and you can also assign IP address to this interface. This type of assignment is not persistent, which means after a reboot of your machine you won’t find a network interface.

Adding a persistent interface and IP address

Adding vr-br.netdev and vr-br.network file in /etc/systemd/network/ directory

sudo touch /etc/systemd/network/vr-br.netdev
sudo touch /etc/systemd/network/vr-br.network

The above command when we run in our system.

ubuntu@ubuntu-exp:~$ sudo touch /etc/systemd/network/vr-br.netdev
ubuntu@ubuntu-exp:~$ sudo touch /etc/systemd/network/vr-br.network
ubuntu@ubuntu-exp:~$ ls /etc/systemd/network/
vr-br.netdev vr-br.network
ubuntu@ubuntu-exp:~$

Edit both the files, I have added the following content in these files.

ubuntu@ubuntu-exp:~$ cat /etc/systemd/network/vr-br.network 
[Match]
Name=vr-br

[Network]
Address=192.168.0.100
Mask=255.255.255.0
ubuntu@ubuntu-exp:~$ 
ubuntu@ubuntu-exp:~$ 
ubuntu@ubuntu-exp:~$ cat /etc/systemd/network/vr-br.netdev 
[NetDev]
Name=vr-br
Kind=dummy
ubuntu@ubuntu-exp:~$ 

For initializing the configuration you can reboot the system or simply run the below-mentioned commands.

sudo systemctl restart systemd-networkd

For testing check the interface with ip a command

ubuntu@ubuntu-exp:~$ sudo systemctl restart systemd-networkd
ubuntu@ubuntu-exp:~$ 
ubuntu@ubuntu-exp:~$ ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: ens3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1450 qdisc fq_codel state UP group default qlen 1000
    link/ether fa:16:3e:6e:46:61 brd ff:ff:ff:ff:ff:ff
    inet 10.0.1.62/8 brd 10.255.255.255 scope global dynamic ens3
       valid_lft 86394sec preferred_lft 86394sec
    inet6 fe80::f816:3eff:fe6e:4661/64 scope link 
       valid_lft forever preferred_lft forever
3: vr-br: <BROADCAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN group default qlen 1000
    link/ether 3a:4f:ec:a3:ad:68 brd ff:ff:ff:ff:ff:ff
    inet 192.168.0.100/24 brd 192.168.0.255 scope global vr-br
       valid_lft forever preferred_lft forever
    inet6 fe80::384f:ecff:fea3:ad68/64 scope link 
       valid_lft forever preferred_lft forever
ubuntu@ubuntu-exp:~$ 

Other tools

We can use ifconfig commands to add a new interface and to manage or play with other network configurations. However, for ifconfig command, we need to install the net-tool package in ubuntu. You can use the following command to install the package.

ubuntu@ubuntu-exp:~$ sudo apt install net-tools