Setting up a Cisco Device – Installing IOS

IOS, as you know refers to Internetwork Operating System which works only on Cisco devices; it comes in the form of binary (.Bin) file. While selecting an IOS image, you have to first check whether it’s compatible with your device.

The naming of the IOS image is done in such a manner that it contains the compatible device name, the version, in which memory the IOS is going to run and the compression type.

PPPPP - FFFF - MM

• ‘P’ refers to the Platform. It’s usually the device name. Keep in mind that it may not be a router always, but can be any Cisco device that runs on an IOS.
• ‘F’ refers to the features. Like n for IPX, d for Desktop Subset etc.
• The first ‘M’ refers to the run time memory, i.e. where the image is going to run on the router. (F-Flash, M-RAM, R-ROM, L-Relocated at run time)
• The second ‘M’ refers to the compression technique used to compress the image so that it can be transferred to the router. (Z-Zip Compression, X-MZIP Compression, W-STAC Compression)

Examples of an image file c3640–ds–mz.

Getting ready to upload an image file:
If you are uploading IOS image file on a fresh device or just upgrading with a latest version, make sure the version of the IOS is compatible with your device and you have enough flash memory. Use ‘show version’ and ‘show flash’ command for this.
In order to upload the IOS file into the device you require a TFTP server. Once you have the TFTP server installed in your system, it has to set in the server mode then ping your Cisco device to check for connectivity. Now you are good to go.

IOS uploading process:
. Launch the TFTP server and set the default directories for upload and download
In the privileged mode, type the command ‘copy tftp flash’. This will copy the IOS file in the upload directory to the flash memory
. When prompted for the address of the remote host, type in the IP address of your system
. And when prompted for the source file name, type in the IOS image file name and add the extension .bin
. Once the erase and upload process is done, the device restarts and boot under the new IOS.

When the IOS is corrupted of erased:
If something goes wrong, like uploading a non compatible IOS image or the image gets corrupted, the devices gets booted in a ‘ROM monitor mode’ which is like the ‘safe mode’ in Windows. This can be identified with the prompt ‘hostname (boot)>’

This is possible because an operating system is loaded in the ROM memory of the device to boot in case the IOS image fails and since this OS is in the ROM memory, there is no question of it getting corrupted.
Now you can continue the process of uploading IOS and make sure you don’t make any mistakes this time.

Some copy commands:
To copy from router to system: R#copy run tftp
To copy from system to router: R#copy tftp run
To copy from flash to system: R#copy flash tftp
To copy from system to flash: R#copy tftp flash
For all the above copy commands to work TFTP server should be running and the router should be able to ping that system.

TFTP servers are small in size and available for free download. There are a lot of free TFTP servers out there, pick one that’s easy to use.
If you are using Windows Visata, you won’t see HyperTerminal in that. You can download this for free from internet.

Cisco IOS Modes of Operation

Commands can be executed in Cisco IOS software under access modes: User and Privileged. The commands in the User mode is in a way, a low level access version of the Privileged mode.

The below table explains the different modes, what can be done in these modes and the prompt telling you which mode you are in.


User mode: You enter this mode when you start a router. You can see ‘Router>’ prompt. Command like ‘ping, telnet, and rlogin’ run in this mode, also you can get information regarding the IOS if you type ‘show version’. So this mode gives you information but does not let you make any modification in the configuration. For any configuration or modification of the router you have to enter into the privileged mode by giving the command ‘enable’

Privileged mode: You will be prompted to enter a password in order to access this mode (while configuring a router for the first time, the password for the privileged mode can be avoided but that’s a security risk). You can modify the router configuration, the interfaces on the router or create an initial configuration following the sub-modes.

In order to make things easier, the sub modes can be identified from the prompt. For example, the privileged mode shows ‘router#’ and if you enter the command ‘configure terminal’ here, the prompt changes to ‘router (config) #’, so this tells you that you are in the ‘Global Configuration Mode’

A list of every command that run in each mode can be displayed by entering ‘?’ while in that particular mode, so this makes things a lot easier. Also you don’t have to type every command, you just have to type the first few letters and let the IOS auto-complete it.
Example: Instead of typing ‘Router#configure terminal’ you can type ‘Router#conf ter’

There are a few Hot Keys that will help you work faster while working on Cisco IOS,

CTRL A	Moves cursor to the beginning of the line
CTRL E	Moves cursor to the end of the line
CTRL B	Moves cursor back one character
CTRL F	Moves cursor forward one character
ESC B	Moves cursor back one word
ESC F	Moves cursor forward one word
CTRL D	Delete one character
Backspace	Delete one character to the left of cursor
CTRL R	Redisplays a line
CTRL V	Erases a line
CTRL W	Erases a word
Ctrl Z	Exits configuration mode
TAB	auto completes partially entered word