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Loopback Interface Operational Mode Commands

Table 1 summarizes the command-line interface (CLI) command that you can use to monitor and troubleshoot the local loopback interface (lo0).

Table 1: Loopback Interface Operational Mode Command

Task

Command

Monitor the loopback interface.

show interfaces (Loopback)

The JUNOS Software automatically configures one local loopback interface (lo0), choosing the first interface to come online as the default. You can also configure the loopback interface and one or more addresses on the interface. If you configure the loopback interface, it is automatically used for unnumbered interfaces.

A local loopback loops packets, including both data and timing information, back on the local Physical Interface Card (PIC) or Physical Interface Module (PIM). When you configure a local loopback, the interface transmits packets to the channel services unit (CSU) built into the interface. These packets are transmitted onto the circuit toward the far-end device. The PIC or PIM receives back its own transmission and ignores any data sent from the physical circuit and the CSU.

To test a local loopback, issue the show interfaces interface-name command. If PPP keepalives transmitted on the interface are received by the PIC or PIM, the Device Flags field contains the output Loop-Detected.

For more information about using the loopback interface to monitor and troubleshoot various interface types, see the JUNOS Interfaces Network Operations Guide.


Published: 2010-04-28

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