Configuring A Loopback Interface - Cisco CISCO851-K9 - 851 Integrated Services Router Configuration Manual

Configuring Basic Parameters

Configuring a Loopback Interface

The loopback interface acts as a placeholder for the static IP address and provides default routing
information.
For complete information on the loopback commands, see the Cisco IOS Release 12.3
documentation set.
Perform these steps to configure a loopback interface:
Command
Step 1 interface type number
Example:
Router(config)# interface Loopback 0
Router(config-int)#
Step 2 ip address ip-address mask
Example:
Router(config-int)# ip address 10.108.1.1
255.255.255.0
Router(config-int)#
Step 3 exit
Example:
Router(config-int)# exit
Router(config)#
Configuration 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 10.10.10.100/24, 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 10.10.10.100 255.255.255.0 (static IP address)
ip nat outside
!
interface Virtual-Template1
ip unnumbered loopback0
no ip directed-broadcast
ip nat outside
!
Cisco 850 Series and Cisco 870 Series Access Routers Software Configuration Guide
1-8
Chapter 1
Purpose
Enters configuration mode for the loopback
interface.
Sets the IP address and subnet mask for the
loopback interface.
Exits configuration mode for the loopback
interface and returns to global configuration
mode.
Basic Router Configuration
OL-5332-01