ESSENTIAL ROUTER COMMANDS | Cisco: A Beginners Guide, Fourth Edition

A few major root commands handle most tasks associated with configuring routers. They include the following:

show Examine router status.
configure Make changes to config file parameters.
no Negate a parameter setting.
copy Put config file changes into effect.

The show command is the bread-and-butter command of IOS. It's used to examine nearly everything about a router and its configuration. The following example shows who's logged into the router, which is moment-to-moment information:

 Router>>show users     Line       User      Host(s)          Idle Location *  2 vty 0              idle              00:00:00

The show command can also be used to show information such as the version of IOS software installed:

 Router>show version Cisco Internetwork Operating System Software IOS (tm) C2600 Software (C2600-ADVIPSERVICESK9-M), Version 12.3(18), RELEASE SOFTWARE (fc3) Technical Support: http://www.cisco.com/techsupport Copyright (c) 1986-2006 by Cisco Systems, Inc. Compiled Wed 15-Mar-06 14:16 by dchih Image text-base: 0x80008098, data-base: 0x81DD1190 ROM: System Bootstrap, Version 12.2(7r) [cmong 7r], RELEASE SOFTWARE (fc1) ROM: C2600 Software (C2600-ADVIPSERVICESK9-M), Version 12.3(18), RE LEASE SOFTWARE (fc3) System returned to ROM by power-on System image file is "flash:c2600-advipservicesk9-mz.123-18.bin"

The no command is used to reverse an existing parameter setting. For example, if we turned on IP accounting for Fast Ethernet port number 1 and now want to turn it off, we point to that interface in configure interface mode-indicated by the MyRouter(config-if)# prompt-and then simply precede the command used to turn it on (ip accounting) with the no command, as shown here:

 MyRouter(config-if)#no ip accounting

Any IOS command can be turned off using the no command syntax.

Knowing how to navigate within an operating system environment is always half the battle. This is especially so in command-line interfaces, because there are no graphical icons to show the way. Table 4-3 lists the commands used to move around within the IOS environment.

Table 4-3: IOS Navigation Commands
Command	Purpose
Enable	Move from User EXEC to Privileged EXEC mode
Disable	Return to User EXEC mode from Privileged EXEC mode
Exit	Exit configuration mode or terminate a login session
CTRL-A	Move to the start of a command line
CTRL-B	Move backward one character position
CTRL-F	Move forward one character position
CTRL-Z	Exit or quit a process (such as a login or a multipage display)
ESC-B	Move to the beginning of the prior word (good for making corrections)
ESC-F	Move to the beginning of the next word

"Hot key" commands are useful because some config-file command lines can get long and complicated.