How to apply Local and Remote loopbacks on the interface

Interface is Down

There are two loopback modes can be configured.

Local loopback

Creates an internal loop on the interface being tested, looping traffic internally on the Physical Interface Card (PIC). 

This can be useful for troubleshooting physical PIC errors and testing the interconnection of the PIC. 

However, it doesn't test the transmit and receive ports. To create a local loopback on an Ethernet interface, 

you can include the loopback statement at the [edit interfaces interface-name (fastether-options | gigether-options)] hierarchy level.

Remote loopback

Ensures link quality between the router and a remote peer during installation or troubleshooting. 

When a remote-loopback request is sent by a remote DTE, the Junos OS places the local interface into loopback mode, 

looping back all frames except OAM PDUs. By default, the remote loopback feature is not enabled.