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Routing & Switching · Foundational

Loopback Interface

A logical, always-up router interface used for management, router IDs and stable peering addresses.

Definition

Loopbacks never go down unless administratively shut, so they provide stable addresses for iBGP peering, LDP and OSPF router IDs. OSPF advertises loopbacks as /32 host routes by default unless the network type is changed to point-to-point. Junos uses lo0 with logical units.

Example

interface Loopback0 / ip address 10.255.0.1 255.255.255.255

Exam tip

iBGP sessions are usually sourced from loopbacks with update-source so they survive physical link failures.

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