Technical Documentation

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. You need to force the link layer to stay up by making some configuration changes to the encapsulation and keepalives.

Force the link layer to stay up, follow these steps:

  1. Configure Encapsulation to Cisco-HDLC
  2. Configure No-Keepalives

Configure Encapsulation to Cisco-HDLC

Action

To set the encapsulation on a T3 physical interface, follow these steps:

  1. In configuration mode, go to the following hierarchy level:
    [edit]user@host# edit interfaces t3-fpc/pic/port:channel
  2. Configure Cisco-HDLC:
    [edit interfaces t3-fpc/pic /port:channel ]user@host# set encapsulation cisco-hdlc
  3. Verify the configuration:
    user@host# show

    For example:

    [edit interfaces t3-0/1/1:8]user@host# show encapsulation hdlc;
  4. Commit the change:
    user@host# commit

    For example:

    [edit interfaces t3-0/1/1:8]user@host# commit commit complete

Meaning

This command sets the interface encapsulation to the Cisco High-level Data-Link Control (HDLC) transport protocol.


Configure No-Keepalives

Action

To disable the sending of link-layer keepalives on a Channelized OC12 or Channelized OC12 IQ interface, follow these steps:.

Note: For a list of interface types associated with the Channelized OC12 IQ interface, see JUNOS Network Interfaces Configuration Guide.

  1. In configuration mode, go to the following hierarchy level:
    [edit]user@host# edit interfaces t3-fpc/pic/port:channel
  2. Configure no-keepalives:
    [edit interfaces t3-fpc/pic/port:channel]user@host# set no-keepalives
  3. Verify the configuration:
    user@host# show

    For example:

    [edit interfaces t3-0/1/1:8]user@host# show no-keepalives;
  4. Commit the change:
    user@host# commit

    For example:

    [edit interfaces t3-0/1/1:8]user@host# commit commit complete

Meaning

By setting no-keepalives, the link layer is forced to stay up. If the setting remains at keepalive, the router will recognize that the same link-layer keepalives are being looped back and will bring the link layer down.


Published: 2010-01-29