Force the Link Layer To Stay Up
To complete the loopback test, the link layer must remain up. However, Junos OS 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.
To force the link layer to stay up, follow these steps:
Configure Encapsulation to Cisco-HDLC
Action
To configure encapsulation on a T3 physical interface, follow these steps:
- In configuration mode, go to the following hierarchy level:[edit]user@host# edit interfaces interface-name
- Configure Cisco-HDLC:[edit interfaces interface-name] user@host# set encapsulation cisco-hdlc
- Verify the configuration:user@host# show
For example:
[edit interfaces t3-1/0/0]user@host# show encapsulation hdlc; - Commit the change:user@host# commit
For example:
[edit interfaces t3-1/0/0]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 T3 physical interface, follow these steps:
- In configuration mode, go to the following hierarchy level:[edit]user@host# edit interfaces interface-name
- Configure no-keepalives:[edit interfaces interface-name]user@host# set no-keepalives
- Verify the configuration:user@host# show
For example:
[edit interfaces t3-1/0/0]user@host# show no-keepalives; - Commit the change:user@host# commit
For example:
[edit interfaces t3-1/0/0]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.
