Cisco CISCO876-SEC-I-K9 Configuration Guide - Page 24

Configuring a Loopback Interface, Configuration Example

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Configuring Basic Parameters Chapter 1 Basic Router Configuration 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: Step 1 Command interface type number Example: Router(config)# interface Loopback 0 Router(config-int)# Purpose Enters configuration mode for the loopback interface. Step 2 ip address ip-address mask Example: Router(config-int)# ip address 10.108.1.1 255.255.255.0 Router(config-int)# Sets the IP address and subnet mask for the loopback interface. Step 3 exit Example: Router(config-int)# exit Router(config)# Exits configuration mode for the loopback interface and returns to global configuration mode. 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 OL-5332-01

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1-8
Cisco 850 Series and Cisco 870 Series Access Routers Software Configuration Guide
OL-5332-01
Chapter 1
Basic Router Configuration
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
Purpose
Step 1
interface
type number
Example:
Router(config)#
interface Loopback 0
Router(config-int)#
Enters configuration mode for the loopback
interface.
Step 2
ip address
ip-address mask
Example:
Router(config-int)#
ip address 10.108.1.1
255.255.255.0
Router(config-int)#
Sets the IP address and subnet mask for the
loopback interface.
Step 3
exit
Example:
Router(config-int)#
exit
Router(config)#
Exits configuration mode for the loopback
interface and returns to global configuration
mode.
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
!