Cisco Systems 520 series manual Loopback interface, Exits configuration mode for the loopback

Chapter 1 Basic Router Configuration

Configuring Basic Parameters

Step 1

Step 2

Step 3

Perform these steps to configure a loopback interface, beginning in global configuration mode:

Command	Purpose
interface type number	Enters configuration mode for the loopback
	interface.
Example:
Router(config)# interface Loopback 0
Router(config-if)#
ip address ip-address mask	Sets the IP address and subnet mask for the
Example:	loopback interface.
Router(config-if)#ip address 10.108.1.1
255.255.255.0
Router(config-if)#
exit	Exits configuration mode for the loopback
	interface and returns to global configuration mode.
Example:
Router(config-if)# 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 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

!

Verifying Your Configuration

To verify that you have properly configured the loopback interface, enter the show interface loopback command. You should see verification output similar to the following example.

Router# show interface loopback 0

Loopback0 is up, line protocol is up

Hardware	is Loopback
Internet	address is 200.200.100.1/24
MTU 1514	bytes, BW 8000000 Kbit, DLY	5000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation LOOPBACK, loopback not		set
Last input never, output never, output hang never
	Cisco Secure Router 520 Series Software Configuration Guide
OL-14210-01			1-7