Modern way to configure dumthe0 in /etc/network/interfaces or similar

configurationnetwork-interfacesystemd

I am looking for a clean, "modern" way to configure, start, and stop the dummy0 network interface (from the dummy kernel module).

My /etc/network/interfaces used to work on an older system but now fails silently on ifup dummy0:

iface dummy0 inet static
   address 10.10.0.1
   netmask 255.255.255.0
   # post-up ip link set dummy0 multicast on

Uncommenting the post-up line produces this error (showing that it runs but that the interface is never created): dummy0: post-up cmd 'ip link set dummy0 multicast on'failed: returned 1 (Cannot find device "dummy0")

This shell script works perfectly but isn't a nice clean config file:

#!/bin/sh
sudo ip link add dummy0 type dummy
sudo ip link set dummy0 multicast on
sudo ip addr add 10.10.0.1/24 dev dummy0
sudo ip link set dummy0 up

My intention is to use it both manually and with a systemd service:

[Service]
Type=oneshot
RemainAfterExit=yes
ExecStart=/sbin/ifup dummy0
ExecStop=/sbin/ifdown dummy0
StandardOutput=syslog+console

Environment:

  • Kubuntu 18.04.2 LTS
  • NetworkManager 1.10.6
  • iproute2 4.15.0
  • ifupdown2 1.0
  • systemd 237 +PAM +AUDIT +SELINUX +IMA +APPARMOR +SMACK +SYSVINIT +UTMP +LIBCRYPTSETUP +GCRYPT +GNUTLS +ACL +XZ +LZ4 +SECCOMP +BLKID +ELFUTILS +KMOD -IDN2 +IDN -PCRE2 default-hierarchy=hybrid

Questions:

  1. How can I convert the shell script into a working /etc/network/interfaces configuration?
  2. Are there any another cleaner or recommended ways to do this?

Best Answer

The interface wasn't "created" previously; ifupdown relied on it magically appearing as soon as the 'dummy' kernel module was loaded. This is old compatibility behavior, and (AFAIIRC) it also interfered with explicit creation of the same interface name, so it was disabled through a module parameter. Now dummy0 has to be created the same way dummy1 or dummyfoobar are created.

You should be able to create the interface in a "pre-up" command:

iface dummy0 inet static
    address 10.10.0.1/24
    pre-up ip link add dummy0 type dummy

If you also use NetworkManager on this system, recent NM versions support dummy interfaces.

nmcli con add type dummy ifname dummy0 ipv4.addresses 10.10.0.1/24 [...]

If the interface should be created on boot and remain forever, that can be done using systemd-networkd (one .netdev configuration to create the device, one .network config to set up IP addresses). However, 'networkctl' still does not have manual "up" or "down" subcommands.

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