Ubuntu 18.04: How to create a persistent dummy network interface

Question

I am trying to create a dummy network interface on a Ubuntu 18.04 server. Here is how I would do it on my previous Ubuntu 16.04 servers:

In /etc/network/interfaces.d/dummy.cfg, write: auto dummy0 iface dummy0 inet static address 192.168.98.1 netmask 255.255.255.0 And then add source /etc/network/interfaces.d/dummy.cfg in /etc/network/interfaces/

From what I understand, Ubuntu 18.04 does not use /etc/network/interfaces anymore, we should use netplan instead. Apparently netplan does not support the creation of virtual interface (!) https://bugs.launchpad.net/ubuntu/+source/nplan/+bug/1743200.

I can create the dummy interface with the iproute2 toolkit instead: $ ip link add dummy0 type dummy $ ip addr add 192.168.98.1/24 dev dummy0 $ ip link set dummy0 up But this interface will disappear after reboot, as one would expect.

How can I create such a dummy network interface that will persist after reboot?

Solution

I had the same problem on 18.04 server and directly used the systemd-networkd way of configuring interfaces:

I created 2 files in /etc/systemd/network/:

1. 10-dummy0.netdev

   [NetDev]
   Name=dummy0
   Kind=dummy
   

2. 20-dummy0.network

   [Match]
   Name=dummy0
   
   [Network]
   Address=192.168....
   Address=fe80::.....
   

On boot the dummy interface is created automatically with IPv4 and IPv6 addresses an is shown in ip addr . Also systemctl restart systemd-networkd should create the interface.

I filed a bug on netplan, please support: https://bugs.launchpad.net/netplan/+bug/1774203

The docs:

https://www.freedesktop.org/software/systemd/man/systemd.netdev.html# https://www.freedesktop.org/software/systemd/man/systemd.link.html# https://www.freedesktop.org/software/systemd/man/systemd.network.html#

Comments

[Arun]

Please check this unix.stackexchange.com/questions/335284/…

[Pierre Mourlanne]

@Arun I checked this question. I already did this configuration, the interfaces are not up on server boot.

[poige]

askubuntu.com/a/1112247/54131

[jpsecher]

On 16.04, I needed to systemctl enable systemd-networkd before the restart.

[SomeOne_1]

The same appears to be the case for later releases of ubuntu. (20.04 as of today)