After setting up the Junos device in configuration mode, you use operational mode to operate your device in the network. Operational mode commands run the device and keep an eye on what the device software and hardware are doing, along with giving you helpful views into the current operations of your overall network.
Even with all the Junos OS commands split between operational and configuration mode, each mode still has hundreds of possible commands. If the CLI showed them all in a single list, it would fill many screens and be difficult to use. So the Junos OS software arranges them into hierarchies that group together related commands (refer to Chapter 2).
Among the most commonly used of the operational hierarchies are the show and clear commands. You use the show command to display status and statistics for just about everything on the device, from the network interfaces (show interfaces) to the hardware (show chassis hardware) to the routing protocols (show ospf, show bgp, and so on). You use the clear command to clear, or zero, statistics collected by the device.
Figure 3-1 shows a sample of hierarchies under the clear and show commands of the operational mode. Notice that both top-level commands have bgp, interfaces, and system commands. Then the next level down has different options in the hierarchies. From these hierarchies, some of the commands available are clear bgp neighbor neighbor-name, show bgp neighbor ...