Loopback Interfaces

We begin our guided tour of interface configuration by assigning the correct IP address to the loopback (lo0) interfaces on your routers. The loopback interface is important because it is the default source of your router ID (RID), and is often used for IBGP peering. Because lo0 is a virtual interface, it represents the most stable IP address on your router.

It should be noted that while Juniper Networks routers permit the configuration of multiple IP addresses on a single logical unit, the router’s loopback interface can only support a single logical unit, and this logical unit must use the default value of 0. Further, M-series routers can only support a single loopback interface instance, and this instance must be identified as 0. The lo0 interface will not support multipoint connectivity so you must be sure to assign a netmask that indicates a full 32 or 128 bits of host address, based on the use of IPv4 or IPv6, respectively.

Note 

Omitting the netmask when assigning a version 4 IP address will result in a default mask of /32 (a host address). This is ideal for loopback interfaces, but will result in commit errors on Ethernet interfaces, because these interfaces are inherently multipoint in nature and therefore will not support the attachment of a single-host device.

Table 2.1 provides the loopback addressing information for r3 and r4:

Table 2.1: Loopback Addressing for r3 and r4

Router

lo0 Address

r3

10.0.3.3/32

r4

10.0.3.4/32




JNCIP. Juniper Networks Certified Internet Professional Study Guide Exam CERT-JNCIP-M
JNCIP: Juniper Networks Certified Internet Professional Study Guide
ISBN: 0782140734
EAN: 2147483647
Year: 2003
Pages: 132

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