Command-Line Interface (CLI)

Because it’s so much more flexible, the CLI (aka Cash Line Interface) truly is the best way to configure a router. To use the CLI, just say No to entering the initial configuration dialog. After you do that, the router will respond with messages that tell you all about the status of each and every one of the router’s interfaces. Here’s an example:

Would you like to enter the initial configuration dialog? [yes/no]:n 

Would you like to terminate autoinstall? [yes]:

Press RETURN to get started!

After the interface status messages appear and you press Enter, the Router> prompt will appear. This is called user exec mode (user mode) and it’s mostly used to view statistics, but it’s also a stepping-stone to logging into privileged mode. You can only view and change the configuration of a Cisco router in privileged exec mode (privileged mode), which you get into with the enable command.

Router con0 is now available 

Press RETURN to get started.

Router>
Router>enable
Router#
Router#

You now end up with a Router# prompt, which indicates that you’re in privileged mode, where you can both view and change the router’s configuration. You can go back from privileged mode into user mode by using the disable command, as seen here:

Router#disable
Router>
Router>logout

Router con0 is now available

Press RETURN to get started.

To configure from a CLI, you can make global changes to the router by typing configure terminal (or config t for short), which puts you in global configuration mode and changes what’s known as the running-config. A global command (a command run from global config) is set only once and affects the entire router.

Router#conf t
Router(config)#

To change the running-config-the current configuration running in dynamic RAM (DRAM)- you use the configure terminal. To change the startup-config-the configuration stored in NVRAM-you use the configure memory command (or config mem for short). If you want to change a router configuration stored on a TFTP host, you use the configure network command (or conf net for short as you already noticed). However, you need to understand that for a router to actually make a change to a configuration, it needs to put that configuration in RAM. So, if you actually type config mem or config net, you’ll replace the current running-config with the config stored in NVRAM or a configuration stored on a TFTP host.

It’s really important that you understand the different prompts you can find when configuring a router. Knowing these well will help you navigate and recognize where you are at any time within configuration mode. In this section, I’m going to demonstrate the prompts that are used on a Cisco router. (Always check your prompts before making any changes to a router’s configuration!). These command prompts really are the ones you’ll use most in real life anyway, plus, they’re the ones you’ll need to know for the exam.

To make changes to an interface, you use the interface command from global configuration mode:

Router(config)#
Router(config)#int [PRESS TAB]
Router(config)#interface ?
Async Async interface
BVI Bridge-Group Virtual Interface
CTunnel CTunnel interface
Dialer Dialer interface
FastEthernet FastEthernet IEEE 802.3
Group-Async Async Group interface
Loopback Loopback interface
MFR Multilink Frame Relay bundle interface
Multilink Multilink-group interface
Null Null interface
Port-channel Ethernet Channel of interfaces
Tunnel Tunnel interface
Vif PGM Multicast Host interface
Virtual-Template Virtual Template interface
Virtual-TokenRing Virtual TokenRing
XTagATM Extended Tag ATM interface
range interface range command

Router(config)#interface Fa [PRESS TAB]
Router(config)#interface FastEthernet 0
Router(config)#interface FastEthernet 0?
/

Router(config)#interface FastEthernet 0/?
<0-1> FastEthernet interface number

Router(config)#interface FastEthernet 0/0 ?
<cr>

Router(config)#interface FastEthernet 0/0
Router(config-if)#

As you already saw in the previous example, you can use <TAB> key and question mark “?” for tips and help in typing the commands into the CLI.

Did you notice that the prompt changed to “Router(config-if)#”? This tells you that you’re in interface configuration mode. Subinterfaces allow you to create logical interfaces within the router. The prompt then changes to “Router(config-subif)#”.

In the following two tables are listed the enhanced editing commands available on a Cisco router and options for Router command history:

Command Meaning
Ctrl + A Moves your cursor to the beginning of the line
Ctrl + E Moves your cursor to the end of the line
Esc + B Moves back one word
Ctrl + B Moves back one character
Ctrl + F Moves forward one character
Esc + F Moves forward one word
Ctrl + D Deletes a single character
Backspace Deletes a single character
Ctrl + R Redisplays a line
Ctrl + U Erases a line
Ctrl + W Erases a word
Ctrl + Z Ends configuration mode and returns to EXEC
Tab Finishes typing a command for you
? Gives you the possible options for finishing the command
Command Meaning
Ctrl + P or Up arrow Shows last command entered
Ctrl + N or Down arrow Shows previous commands entered
show history Shows last 10 commands entered by default
show terminal Shows terminal configurations and history buffer size
terminal history size Changes buffer size (max 256)

The show version command will provide basic configuration for the system hardware as well as the software version, the names and sources of configuration files, and the boot images. Here’s an example:

Router#sh ver
Cisco Internetwork Operating System Software
IOS (tm) 3700 Software (C3745-ADVIPSERVICESK9-M), Version 12.3(22), RELEASE SOFTWARE (fc2)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2007 by cisco Systems, Inc.
Compiled Wed 24-Jan-07 18:55 by ccai
Image text-base: 0x60008AF4, data-base: 0x61F60000

ROM: ROMMON Emulation Microcode
ROM: 3700 Software (C3745-ADVIPSERVICESK9-M), Version 12.3(22), RELEASE SOFTWARE (fc2)

Router uptime is 1 hour, 42 minutes
System returned to ROM by unknown reload cause – suspect boot_data[BOOT_COUNT] 0x0, BOOT_COUNT 0, BOOTDATA 19
System image file is “tftp://255.255.255.255/unknown”

This product contains cryptographic features and is subject to United
States and local country laws governing import, export, transfer and
use. Delivery of Cisco cryptographic products does not imply
third-party authority to import, export, distribute or use encryption.
Importers, exporters, distributors and users are responsible for
compliance with U.S. and local country laws. By using this product you
agree to comply with applicable laws and regulations. If you are unable
to comply with U.S. and local laws, return this product immediately.

A summary of U.S. laws governing Cisco cryptographic products may be found at:
http://www.cisco.com/wwl/export/crypto/tool/stqrg.html

If you require further assistance please contact us by sending email to
export@cisco.com.

cisco 3745 (R7000) processor (revision 2.0) with 121856K/9216K bytes of memory.
Processor board ID XXXXXXXXXXX
R7000 CPU at 100MHz, Implementation 39, Rev 2.1, 256KB L2, 512KB L3 Cache
Bridging software.
X.25 software, Version 3.0.0.
2 FastEthernet/IEEE 802.3 interface(s)
DRAM configuration is 64 bits wide with parity enabled.
151K bytes of non-volatile configuration memory.
16384K bytes of ATA System CompactFlash (Read/Write)

Configuration register is 0x2142

Tip: “show version” and “show running-config” are the commands with which you can create backup information about a router. The first one will give you the information about the hardware and the attached modules into the chassis, while the socond one command will create a script with your (probably) working configuration.

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