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.
To force the link layer to stay up, follow these
steps:
To configure encapsulation on a T3 physical interface, follow
these steps:
In configuration mode, go to the following hierarchy level:
[edit]
user@host# edit interfacesinterface-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.
