Friday, April 2, 2010


The IOS stands for the Internetwork Operating System. It is the operating system of Cisco. It is a command set to set up any Cisco device. Cisco calls themselves a software vendor. All vendors can produce the same hardware as all other companies, but it's the IOS that makes them stand out.
The operating system used on a Cisco Firewall resembles the IOS, but it's not the IOS. It's a different operating system because they wouldn't want any IOS vulnerability to carry over to their Firewalls. However, they are made to look and feel like the IOS.

To connect to a Cisco Switch or Router, you'll have to get a console cable. A console cable is a rollover cable that terminates to a serial port behind your computer. The RJ-45 side is plugged into the console port of the Switch or Router.

To access the console, you'll have to use a console program like:
-Hyper Terminal
-Tera Term

The settings to connect are:
-Baud Rate: 9600
-Data Bits: 8
-Parity: None
-Stop Bits: 1
-Flow Control: None

At any time you want to know what to type next, you can make use of the context sensitive help by hitting "?". You can perform auto-complete (up to the most generalized match) by hitting tab. From there, you can hit "?" again to see all possible commands. The "?" also works during certification examinations. In a context sensitive help, anything in capital letters, such as MONTH, will require you to type in a String.

When you first get into a Cisco device, you get into the User Mode:

The &gt sign tells you that you're in the User Mode. In the User Mode, you can only do pings, certain show commands, and other basic commands.

To do more things, you'll have to enter the Privileged Mode. To enter the Privileged Mode, enter:

Notice that your prompt will look like:

From the Privileged Mode, you can view a lot of things (including the running configuration and passwords). But that's all you can do from Privileged Mode. To really configure the router, you'll have to enter the Global Configuration Mode. To be in the Global Configuration Mode, you'll need to enter this while Privileged:
conf t

Now your prompt should look like:

From the Global Configuration Mode, you can do things like:
ho C2950

To enter an interface, you'll have to be in Global Configuration Mode. To modify f0/1, type:
in f0/1

You'll be in the interface prompt, which looks like:

Notice that you moved into the interface mode through:
Privileged Mode > Global Configuration Mode > Interface Mode

To move back one level at a time, use:

To move all the way back to Privileged Mode, use:

If you type something wrong, it'll tell you where the error is with a caret. Note that User Mode can also be known as User Exec. Privileged Mode is also known as Privileged Exec.

Like any other command line interfaces, hitting the UP arrow would cycle through previous commands. To move to the end of the line, use CTRL+E, and to move to the start, use CTRL+A. To see the last 10 commands typed, use:
show history

To type characters like "?", use CTRL+V, then hit "?". CTRL+V acts as an escape character. Typing "no" in front of any command would typically move that configuration. When a line gets too long, the IOS will hide things at the front or back with the "$" sign. $ means that there are more stuff either to the left or the right depending on where it is.

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