Basics of Cisco IOS Command-line

Cisco IOS Operating System Software has shortcuts for entering commands.

For example, the command for moving from user mode to enable mode, is "enable", which can also be typed as "en".

Short form of a command is sufficient for Cisco routers and switches, as long as there is no ambiguity. You can also use the tab key to auto complete the command as in Unix based Operating Systems.


The Cisco IOS Operating System "enable" command

The Cisco IOS Operating System "enable" command is used to move a user from User mode to Privileged mode.

Router>enable
Router#

The Cisco IOS Operating System "exit" command

The Cisco IOS Operating System "exit" command, moves the user back to one level.

For example, if the user is in Global Configuration mode, the "exit" command will take you to Privileged mode.


Router(config-if)#exit
Router (config)#

 The Cisco IOS Operating System "disable" command

The Cisco IOS Operating System "disable" command moves you from privileged mode back to user mode.


Router#disable
Router>


 The Cisco IOS Operating System Setup Mode

The Cisco IOS Operating System Setup Mode starts automatically if no startup configuration present. The "Control+C" key combination at any time will end the setup process, shut down all interfaces, and take you to user mode (Router>). Changing the Cisco IOS Operating System using setup mode is not a recommended practice. Instead, you should use the command-line interface (CLI), which is more powerful.


 The Cisco IOS Operating System Command-line history

We can use the up arrow or down arrow to recall commands in the history buffer in a backward or forward sequence.

The Cisco IOS Operating System show commands

The IOS show commands are very helpful to view the information available in a Cisco Router or Switch.

Following are the most commonly used Cisco IOS show commands.

• Router#show version  (Displays information about current IOS)

• Router#show flash  (Displays information about Flash memory)

• Router#show history  (Lists all commands in the history buffer)

To view all possible show commands type “show ?” at the prompt. Note, you will be able to see more show commands when using enable mode. The possible enabled show commands are displayed in the output below:

Router#show ?
  access-expression  List access expression
  access-lists       List access lists
  accounting         Accounting data for active sessions
  aliases            Display alias commands
  appletalk          AppleTalk information
  arap               Show Appletalk Remote Access statistics
  arp                ARP table
  async              Information on terminal lines used as router interfaces
  backup             Backup status
  bridge             Bridge Forwarding/Filtering Database [verbose]
  buffers            Buffer pool statistics
  cdp                CDP information
  clock              Display the system clock
  compress           Show compression statistics
  configuration      Contents of Non-Volatile memory
  controllers        Interface controller status
  debugging          State of each debugging option
  decnet             DECnet information
  dhcp               Dynamic Host Configuration Protocol status
  dialer             Dialer parameters and statistics
  dnsix              Shows Dnsix/DMDP information
  dxi                atm-dxi information
  entry              Queued terminal entries
  file               Show filesystem information
  flash:             display information about flash: file system
  flh-log            Flash Load Helper log buffer
  frame-relay        Frame-Relay information
  history            Display the session command history
  hosts              IP domain-name, lookup style, nameservers, and host table
  interfaces         Interface status and configuration
  ip                 IP information
  ipx                Novell IPX information
  key                Key information
  line               TTY line information
  llc2               IBM LLC2 circuit information
  location           Display the system location
  logging            Show the contents of logging buffers
  memory             Memory statistics
  modemcap           Show Modem Capabilities database
  ntp                Network time protocol
  ppp                PPP parameters and statistics
  printers           Show LPD printer information
  privilege          Show current privilege level
  processes          Active process statistics
  protocols          Active network routing protocols
  queue              Show queue contents
  queueing           Show queueing configuration
  registry           Function registry information
  reload             Scheduled reload information
  rhosts             Remote-host+user equivalences
  rif                RIF cache entries
  rmon               rmon statistics
  route-map          route-map information
  rtr                Response Time Reporter (RTR)
  running-config     Current operating configuration