Junos® OS For Dummies®, 2nd Edition

Using Diagnostic Commands

You'll find yourself using the same commands again and again to monitor, troubleshoot, and diagnose your network. These commands are the show commands that display important information about your interfaces and your routing (next-hop or forwarding) tables.

Almost every feature within the Junos OS software comes with corresponding show commands so that you can see what is happening on the device. Here are the show commands that you'll use most frequently:

• show interfaces
• show route
• show <protocol>

The following sections cover each of these commands in detail.

Monitoring your interfaces

You'll often want to look at how your interfaces are behaving to figure out what is happening to the traffic within your device. As such, you need to become an expert in the show interfaces command.

As with all show commands, this command has several variations:

• show interfaces (no modifier): The show interfaces command, issued with no modifier, gives you a summary of some of the most important fields and counters tracked for interfaces. This command is an excellent starting point for most interface activities.
• show interfaces brief: The brief version of the same command pares down the output even more. This command is useful when you're looking for big things such as whether an interface is up. If you need detailed statistics or counters, you must delve a little deeper than the brief command.
• show interfaces detail: The detailed output for show interfaces includes all ...