Step 4: Force the Link Layer to Stay Up
Purpose
To complete the loopback test, the link layer must remain up. However, JUNOS software is designed to recognize that loop connections are not valid connections and to bring the link layer down. If you have the Point-to-Point protocol (PPP) configured, you need to change the encapsulation to Cisco High-level Data Link Control (HDLC) and reconfigure the keepalives in order to force the link layer to stay up.
Steps To Take