Interface Loopback - Juniper JUNOSE 11.1.X - COMMAND REFERENCE A TO M 4-9-2010 Command Reference Manual

JUNOSe 11.1.x Command Reference Guide A to M

interface loopback

[ no ] interface loopback interfaceSpecifier
Syntax
Command introduced before JUNOSe Release 7.1.0.
Release Information
Defines a loopback interface, which provides a stable address for protocols (for
Description
example, BGP, Telnet, or LDP) to use so that they can avoid any impact if a physical
interface goes down. The loopback interface sends packets back to the router or
access server for local processing. Any packets routed from the loopback interface,
but not destined to the loopback interface, are dropped. The no version deletes the
loopback interface.
NOTE: Do not confuse loopback with the null 0 interface. Traffic routed to null 0 is
discarded on the line module.
You cannot shut down a loopback interface.
BEST PRACTICE: We recommend that you configure a 32-bit subnet mask for the
loopback interface. For example, if you configure a loopback interface with the IP
address and mask as 1.1.1.1/16, the 1.1.0.0/16 route entry is entered on the line
module and if no specific or longer route entry is found, all traffic destined to the to
1.1.0.0/16 subnet is forwarded to the SRP module by the line module. Although the
SRP module responds only to traffic destined to the 1.1.1.1 subnet and discards
traffic to all other host IP addresses within that subnet (1.1.1.1/16), if the SRP module
receives too much traffic from subnets other than 1.1.1.1, the CPU utilization on the
SRP module reaches the saturation level.
Options
Global Configuration
Mode
Related Topics
726
interface loopback
interfaceSpecifier—Particular interface; format varies according to interface type;
see Interface Types and Specifiers on page 5
Configuring an MPLS Pseudowire with VCC Cell Relay Encapsulation, Configuring
Local ATM Cross-Connects with AAL5 Encapsulation, Configuring Local
Cross-Connects Between Ethernet/VLAN Interfaces, Configuring the Loopback
Interface and Router ID for BGP for L2VPNs, and Configuring the Loopback Interface
and Router ID for VPLS in the JUNOSe BGP and MPLS Configuration Guide