Networking

You don't need a CCNA to maintain your Cisco router

If your Cisco router is somewhat foreign territory, these tips will come in handy. Learn how to use some common commands and built-in help that are available in the two modes of operation.


As network administrator, you're supposed to know everything. But the fact is, you don't. Take that router, for example. It's a sophisticated piece of equipment running its own operating system that needs to be kept up to date. It helps to secure your network and houses an abundance of information about the health of your network. But if you don't have a CCNA, you may try to ignore it or rely on someone else to perform some router magic.

The truth is, you don't have to be CCNA-certified to do basic router maintenance or to explore the network information routers contain. In this article and the next two, I'll explain what you need to know to find your way around your router and perform some basic tasks. Think of it as a survival guide for non-CCNA network administrators. I'll start here by introducing common commands and built-in help options available in the two types of Exec mode, User Exec, and Privileged Exec.

Getting around in the User Exec mode
Begin by logging on to the router. Press [Enter] to start and you are greeted by the prompt:
 
RouterName>

You are now in the User Exec mode of the Exec command interpreter (the command line interface). This mode is identified by the > prompt. In this basic mode, you can connect to other devices and display system information, but you can't make any changes.

A few built-in tools can help you find your way around the router. The question mark is one of them. To get a list of all router commands available in this mode, just type a question mark at the prompt to display the list of commands shown in Table A.
Table A
Commands in the User Exec mode
disable Turn off privileged commands
disconnect Disconnect an existing network connection
enable Turn on privileged commands
exit Exit from the EXEC
help Description of the interactive help system
logout Exit from the EXEC
ping Send echo messages
show Show running system information

You can also use the question mark to get help on a specific command. For instance, take the show command in the output above. When you type show ?, you'll see the commands you can use with show in User Exec mode (Table B).
Table B
Show commands
arp ARP table
cdp CDP information
clock Display the system clock
controllers Interface controller status
flash Display information about flash: file system
frame-relay Frame-Relay information
history Display the session command history
hosts IP domain-name, nameservers, and host table
interfaces Interface status and configuration
ip IP information
ipx Novell IPX information
isdn ISDN information
ntp Network time protocol
protocols Active network routing protocols
running-config Current operating configuration
sessions Information about Telnet connections
startup-config Contents of startup configuration
terminal Display terminal configuration parameters
users Display information about terminal lines
version System hardware and software status

As you can see, the show command is a powerful tool and a useful source of configuration information. You can also use the show command and the question mark to figure out other commands. For example, if you knew that a command started with c but you couldn't recall its name, you could type:
 
Showc?

The router would then list the commands starting with c:
 
cdp clock controllers

Placing the question mark immediately after the partial command completes the command. Leaving a space before the question mark tells the command line interpreter (CLI) that you are looking for the next command parameter and not for the rest of a command, as in the previous example. So if you type:
 
show controllers ?

the router will offer:
serial

which tells you to type:
show controllers serial

to display serial controllers info.

Helpful shortcuts
To give you a break from all this command line typing, Cisco offers a [Tab] key shortcut. Take that long word controllers. If you type:
 
show con

and press [Tab], the CLI will complete the command. You can abbreviate most of the router commands as long as they're unambiguous. For example, instead of typing show, you can type sh. Because no other command starts with sh, the CLI knows you mean show and obliges by displaying the appropriate information.

The show command also allows you to recall the command history, so you can copy, edit, or remove commands—which is especially helpful if they're long and complicated. To show the history of commands entered, type
 
show history

To edit commands, you can use the left arrow key to move back one character at a time, the right arrow to move forward one character at a time, the up arrow to recall the previous command, and the down arrow to recall the most recent command. (So the up and down arrows will scroll through the history of commands.) [Ctrl]A moves you to the beginning of a line and [Ctrl]E moves you to the end.

Working in Privileged Exec mode
The other, more powerful mode of the Exec command interpreter is Privileged Exec (also called Enable Exec) mode. This mode supports the same editing and help commands as User Exec mode, but you have access to many more functions and information. It is also the mode for debugging and for updating and changing the router's configuration, including interfaces, such as serial and Ethernet; IPX and routing protocols such as RIP and IGRP; access lists; and WAN protocols such as X.25, Frame Relay, ISDN/LAPD, HDLC, and PPP. In addition, this mode allows you to troubleshoot IP packet detail and IP routing.

To enter this mode from the User Exec mode, type enable and press [Enter]:
 
RouterName>enable

You'll know you're in Privileged Exec mode when you see the hash prompt:
 
RouterName#

In my next article, I'll take a closer look at the tasks you can complete in Privileged Exec mode.

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