Loopback Interfaces

This chapter tells how to configure loopback interfaces.

About Loopback Interfaces

A loopback interface is a software-only interface that emulates a physical interface. This interface is reachable on IPv4 and IPv6 through multiple physical interfaces. The loopback interface helps to overcome path failures; it is accessible from any physical interface, so if one goes down, you can access the loopback interface from another.

Loopback interfaces can be used for:

  • AAA

  • BGP

  • SNMP

  • SSH

  • Syslog

  • Telnet

The ASA can distribute the loopback address using dynamic routing protocols, or you can configure a static route on the peer device to reach the loopback IP address through one of the ASA's physical interfaces. You cannot configure a static route on the ASA that specifies the loopback interface.

Guidelines for Loopback Interfaces

Failover and Clustering

  • No clustering support.

Context Mode

  • VTI is supported in single context mode only. Other loopback uses are supported in multiple context mode.

Additional Guidelines and Limitations

  • TCP sequence randomization is always disabled for traffic from the physical interface to the loopback interface.

Configure a Loopback Interface

Add a loopback interface.

Procedure

Step 1

Choose Configuration > Device Setup > Interface Settings > Interfaces.

Step 2

Choose Add > Loopback Interface.

The Add Loopback Interface dialog box appears.

Step 3

In the Loopback ID field, enter an integer between 0 and 10413.

Step 4

Enter the IP address and subnet mask.

Step 5

If the interface is not already enabled, check the Enable Interface check box.

The interface is enabled by default.

Step 6

Enter a description in the Description field.

Step 7

Click the IPv6 tab to add an IPv6 address.

  1. Click Add and enter the IPv6 address.

  2. (Optional) Check the EUI 64 check box to configure IPv6 with EUI-64.

  3. Click OK.

Step 8

Click OK.

You return to the Interfaces pane.

History for Loopback Interfaces

Table 1. History for Loopback Interfaces

Feature Name

Version

Feature Information

Support for loopback interface

9.18(2)

You can now add a loopback interface and use it for:

  • BGP

  • AAA

  • SNMP

  • Syslog

  • SSH

  • Telnet

New/Modified commands: interface loopback , logging host , neighbor update-source , snmp-server host , ssh , telnet

No ASDM support.