Dummy

The dummy interface is really a little exotic, but rather useful nevertheless. Dummy interfaces are much like the Loopback interface, except you can have as many as you want.

Note

Dummy interfaces can be used as interfaces that always stay up (in the same fashion to loopbacks in Cisco IOS), or for testing purposes.

Hint

On systems with multiple redundant uplinks and routes, it’s a good idea to use a dedicated address for management and dynamic routing protocols. However, assigning that address to a physical link is risky: if that link goes down, that address will become inaccessible. A common solution is to assign the management address to a loopback or a dummy interface and advertise that address via all physical links, so that it’s reachable through any of them. Since in Linux-based systems, there can be only one loopback interface, it’s better to use a dummy interface for that purpose, since they can be added, removed, and taken up and down independently.

Configuration

Common interface configuration

set interfaces dummy <interface> address <address>

Configure interface <interface> with one or more interface addresses.

  • address can be specified multiple times as IPv4 and/or IPv6 address, e.g. 192.0.2.1/24 and/or 2001:db8::1/64

Example:

set interfaces dummy dum0 address 192.0.2.1/24
set interfaces dummy dum0 address 2001:db8::1/64
set interfaces dummy <interface> description <description>

Set a human readable, descriptive alias for this connection. Alias is used by e.g. the show interfaces command or SNMP based monitoring tools.

Example:

set interfaces dummy dum0 description 'This is an awesome interface running on VyOS'
set interfaces dummy <interface> disable

Disable given <interface>. It will be placed in administratively down (A/D) state.

Example:

set interfaces dummy dum0 disable
set interfaces dummy <interface> vrf <vrf>

Place interface in given VRF instance.

See also

There is an entire chapter about how to configure a VRF, please check this for additional information.

Example:

set interfaces dummy dum0 vrf red

Operation

show interfaces dummy

Show brief interface information.

vyos@vyos:~$ show interfaces dummy
Codes: S - State, L - Link, u - Up, D - Down, A - Admin Down
Interface        IP Address                        S/L  Description
---------        ----------                        ---  -----------
dum0             172.18.254.201/32                 u/u
show interfaces dummy <interface>

Show detailed information on given <interface>

vyos@vyos:~$ show interfaces ethernet eth0
dum0: <BROADCAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN group default qlen 1000
    link/ether 26:7c:8e:bc:fc:f5 brd ff:ff:ff:ff:ff:ff
    inet 172.18.254.201/32 scope global dum0
       valid_lft forever preferred_lft forever
    inet6 fe80::247c:8eff:febc:fcf5/64 scope link
       valid_lft forever preferred_lft forever

    RX:  bytes    packets     errors    dropped    overrun      mcast
             0          0          0          0          0          0
    TX:  bytes    packets     errors    dropped    carrier collisions
       1369707       4267          0          0          0          0