Live Experience

Loopback Test on a T1 Interface in Juniper
A new T1 interface has been installed and configured, and you want to perform a loopback test to make sure the interface is operating properly.
Set up a T1 loopback configuration:
[edit interfaces t1-0/0/3 ]
source@RouterF# set t1-options loopback local 
source@RouterF# set no-keepalives 
source@RouterF# set encapsulation cisco-hdlc 
source@RouterF# commit 
Make sure the interface is up:
source@RouterF> show interfaces t1-0/0/3 terse
Interface               Admin    Link  Proto    Local     Remote
t1-0/0/3                up       up
Then zero all the statistics on the interface:
source@RouterF> clear interfaces statistics t1-0/0/3
Run the loopback test, which sends 100 ping messages rapidly and reports the results in a single message:
source@RouterF> ping interface t1-0/0/3 bypass-routing count 1000 rapid
PING ( 56 data bytes
--- ping statistics --
100 packets transmitted, 1000 packets received, 0% packet loss
round-trip min/avg/max/stddev = 2.376/19.102/369.920/35.795 ms
To perform a loopback test on the T1 interface, first configure the T1 interface to use local loopback mode. Also include the encapsulation cisco-hdlc and no-keepalives statements to force the interface to stay up so you can run the ping loopback test. Then you need to create a physical loopback at the T1 port by connecting a T1 loopback plug to the T1 port. You can make a T1 loopback plug by connecting pin 1 to pin 4 and pin 2 to pin 5 on an RJ-48 plug.
source@RouterF> show interfaces t1-0/0/3 extensive
If there are any problems on the link, you see input and output errors in the show interfaces extensive command output. This output also shows that 100 ping messages were sent (in Output packets) and 100 responses were received (in Input packets).
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