Interfaces and Hardware Component Configuration Guide for Cisco 8000 Series Routers, Cisco IOS XR Releases

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Interfaces and Hardware Component Configuration Guide for Cisco 8000 Series Routers, Cisco IOS XR Releases

Configure virtual loopback interfaces

Updated: July 31, 2026

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This topic describes how to configure a basic virtual loopback interface on the Cisco 8000 Series Router.

Use this procedure to configure a basic virtual loopback interface to serve as an always-up endpoint for routing protocol sessions or as a target for ping-based reachability verification.

Procedure

1.

Enter global configuration mode using the configure command.

Example:

Router# configure
2.

Enter interface configuration mode and name the new loopback interface.

Example:

Router(config)# interface Loopback 3
3.

Assign an IP address and subnet mask to the virtual loopback interface.

Example:

Router(config-if)# ipv4 address 172.18.189.38/32
4.

Save the configuration changes using the end or commit command.

Example:

Router(config-if)# end

When you issue the end command, the system prompts you to commit changes:

Uncommitted changes found, commit them before exiting(yes/no/cancel)?
[cancel]:

  • Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.

  • Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.

  • Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.

  • Use the commit command to save the configuration changes to the running configuration file and remain within the configuration session.
5.

(Optional) Display the configuration of the loopback interface.

Example:

Router# show interfaces Loopback 3
6.

Use the show interfaces Loopback command to verify the configuration.

Example:

Router# configure
Router(config)# interface Loopback 3
Router(config-if)# ipv4 address 172.18.189.38/32
Router(config-if)# end
Uncommitted changes found, commit them? [yes]: yes
Router# show interfaces Loopback 3

Loopback3 is up, line protocol is up
 Hardware is Loopback interface(s)
 Internet address is 172.18.189.38/32
 MTU 1514 bytes, BW Unknown
   reliability 0/255, txload Unknown, rxload Unknown
 Encapsulation Loopback, loopback not set
 Last clearing of "show interface" counters never
 5 minute input rate 0 bits/sec, 0 packets/sec
 5 minute output rate 0 bits/sec, 0 packets/sec
   0 packets input, 0 bytes, 0 total input drops
   0 drops for unrecognized upper-level protocol
   Received 0 broadcast packets, 0 multicast packets
   0 packets output, 0 bytes, 0 total output drops
   Output 0 broadcast packets, 0 multicast packets

Guidelines and restrictions for configuring virtual loopback interfaces

Observe the following restrictions when you configure a virtual loopback interface:

  • The IP address of a loopback interface must be unique across all routers on the network.

  • That IP address must not be used by another interface on the router.

  • The IP address must not be used by an interface on any other router on the network.