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Cisco 880 Series Integrated Services Router Software Configuration Guide
OL-22206-01
Chapter 3 Basic Router Configuration
Configuring a Loopback Interface
Configuring a Loopback Interface
The loopback interface acts as a placeholder for the static IP address and provides default routing
information.
To configure a loopback interface perform these steps, beginning in global configuration mode:
SUMMARY STEPS
1. interface type number
2. ip address ip-address mask
3. exit
DETAILED STEPS
Example
The loopback interface in this sample configuration is used to support Network Address Translation
(NAT) on the virtual-template interface. This configuration example shows the loopback interface
configured on the Fast Ethernet interface with an IP address of 200.200.100.1/24, which acts as a static
IP address. The loopback interface points back to virtual-template1, which has a negotiated IP address.
!
interface loopback 0
ip address 200.200.100.1 255.255.255.0 (static IP address)
ip nat outside
!
interface Virtual-Template1
ip unnumbered loopback0
no ip directed-broadcast
ip nat outside
!
Command Purpose
Step 1
interface type number
Example:
Router(config)# interface Loopback 0
Router(config-if)#
Enters configuration mode for the loopback
interface.
Step 2
ip address ip-address mask
Example:
Router(config-if)# ip address 10.108.1.1
255.255.255.0
Router(config-if)#
Sets the IP address and subnet mask for the
loopback interface.
Step 3
exit
Example:
Router(config-if)# exit
Router(config)#
Exits configuration mode for the loopback
interface and returns to global configuration
mode.