Dummy

A dummy interface is a virtual network interface that operates like the loopback interface, accepting traffic and routing it back to the local host. Unlike the loopback interface, which is limited to one per system and reserved for internal system use, multiple dummy interfaces can be created, removed, and managed without impacting core operations.

As a software-based interface, the dummy interface does not depend on physical link state and remains active as long as the operating system is running.

Dummy interfaces are commonly used in environments with multiple redundant uplinks (e.g., a server connected to two different switches), where assigning a management IP address to a specific physical interface is risky. If that interface fails, the management IP address becomes unreachable.

Assigning the management IP address to a dummy interface and advertising it over all available physical links ensures the address remains reachable as long as at least one physical path is active.

Dummy interfaces are also used for testing and simulation purposes.

Configuration

Common interface configuration

set interfaces dummy <interface> address <address>

Configure one or more interface IP addresses.

<address> supports IPv4 and IPv6 in CIDR notation. For example, use 192.0.2.1/24 for IPv4 or 2001:db8::1/64 for IPv6.

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>

Configure a clear, descriptive alias for the interface.

This alias appears in the show interfaces command and SNMP-based monitoring tools.

Example:

set interfaces dummy dum0 description 'This is an interface running on VyOS.'

set interfaces dummy <interface> disable

Disable the interface.

The interface will be set to the administratively down (A/D) state.

Example:

set interfaces dummy dum0 disable

set interfaces dummy <interface> vrf <vrf>

Assign the interface to a specific VRF instance.

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 interface information.

vyos@vyos:~$ show interfaces dummy dum0
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