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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?
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  • @sourcejedi Thanks, I'll update my post! Commented Apr 20, 2019 at 21:18

2 Answers 2

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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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Recently I needed bring two dummy interfaces on Oracle Linux 8 (standard 4.18 kernel). Automatic cleaning config files don't critical for me and I used Oleg's idea and theirs script on first post this thread and script for NetworkManager from the article Dummy interface on RHEL and wrote two simple scripts for bring up with startup two dummy interfaces

  • Load dummy module 
    # echo "dummy" > /etc/modules-load.d/dummy.conf
  • Determinate two dummy interfaces 
    # echo "options dummy numdummies=2" > /etc/modprobe.d/dummy.conf

Created two script - for example 98-dummy0 and example 99-dummy1- in /etc/NetworkManager/dispatcher.d/ directory:

98-dummy0

#!/bin/sh # See the "DISPATCHER SCRIPTS" section of `man NetworkManager`. # Remember to make this file executable! # Create the dummy interface. /sbin/ip link add dummy0 type dummy /sbin/ip link set dummy0 multicast on /sbin/ip addr add 10.10.0.1/24 dev dummy0 /sbin/ip link set dummy0 up

For 99-dummy1 change IP adress to 10.10.0.2/24 and rename to dummy1.

Reboot and check

[mvg@oracle ~]$ ifconfig dummy0: flags=4291<UP,BROADCAST,RUNNING,NOARP,MULTICAST> mtu 1500 inet 10.10.0.1 netmask 255.255.255.0 broadcast 0.0.0.0 inet6 fe80::e4b7:27ff:fe33:73e9 prefixlen 64 scopeid 0x20<link> ether e6:b7:27:33:73:e9 txqueuelen 1000 (Ethernet) RX packets 0 bytes 0 (0.0 B) RX errors 0 dropped 0 overruns 0 frame 0 TX packets 84 bytes 10858 (10.6 KiB) TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0 dummy1: flags=4291<UP,BROADCAST,RUNNING,NOARP,MULTICAST> mtu 1500 inet 10.10.0.2 netmask 255.255.255.0 broadcast 0.0.0.0 inet6 fe80::7c8a:e7ff:feee:b648 prefixlen 64 scopeid 0x20<link> ether 7e:8a:e7:ee:b6:48 txqueuelen 1000 (Ethernet) RX packets 0 bytes 0 (0.0 B) RX errors 0 dropped 0 overruns 0 frame 0 TX packets 78 bytes 10306 (10.0 KiB) TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0 enp3s0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500 inet 192.168.1.131 netmask 255.255.255.0 broadcast 192.168.1.255 inet6 fdb0:34c:6e16:0:a01e:6127:6aa7:1bba prefixlen 64 scopeid 0x0<global> inet6 fe80::2cd7:76d7:c757:6b30 prefixlen 64 scopeid 0x20<link> ether 94:de:80:07:50:d2 txqueuelen 1000 (Ethernet) RX packets 15759 bytes 14474446 (13.8 MiB) RX errors 0 dropped 0 overruns 0 frame 0 TX packets 11577 bytes 1411688 (1.3 MiB) TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0 lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536 inet 127.0.0.1 netmask 255.0.0.0 inet6 ::1 prefixlen 128 scopeid 0x10<host> loop txqueuelen 1000 (Local Loopback) RX packets 112 bytes 9480 (9.2 KiB) RX errors 0 dropped 0 overruns 0 frame 0 TX packets 112 bytes 9480 (9.2 KiB) TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0 virbr0: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500 inet 192.168.122.1 netmask 255.255.255.0 broadcast 192.168.122.255 ether 52:54:00:6b:09:b3 txqueuelen 1000 (Ethernet) RX packets 0 bytes 0 (0.0 B) RX errors 0 dropped 0 overruns 0 frame 0 TX packets 0 bytes 0 (0.0 B) TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

Either dummy interface pinged.

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