Step 5: Check That the Received and Transmitted Path Trace Are the Same

Purpose

The received and transmitted path trace shows whether the transmitted path trace is looped back.

Action

To check that the received path trace matches the transmitted path trace, use the following JUNOS CLI operational mode command:

user@host> show interfaces so-fpc/pic/port extensive 

Sample Output

user@host# show interfaces so-2/2/0 extensive

Physical interface: so-2/2/0, Enabled, Physical link is Up

Interface index: 21, SNMP ifIndex: 45, Generation: 20

[...Output truncated...]

Received path trace: host so-2/2/0

70 6c 75 74 6f 6e 69 63 20 73 6f 2d 32 2f 32 2f   host so-2/2/

30 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   0...............

00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   ................

00 00 00 00 00 00 00 00 00 00 00 00 00 00 0d 0a   ................

Transmitted path trace: host so-2/2/0

70 6c 75 74 6f 6e 69 63 20 73 6f 2d 32 2f 32 2f   host so-2/2/

30 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   0...............

00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   ................

00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   ................

[...Output truncated...]

What It Means

This transmitted and received path trace information is near the end of the output. The sample output shows that the transmitted and received path trace are the same. When there is a loopback, the transmitted and received path trace should be the same. If they are, continue with Force the Link Layer to Stay Up.

If the transmitted and received path trace are not the same, the physical loopback cable is probably on the wrong port, or is incorrectly connected. In this case, verify the connection again.