PuTTY basic commands

IOS Commands 1Since the release of the Cisco CCENT Exam (ICND1: 640-822), I have written a number of articles concentrating on the exam objectives for this new certification.

In today's article, I will give you a short introduction to the Cisco Internetwork Operating System, also known as the IOS. This is the operating system that controls Cisco routers and switches and provides the interface to configure Cisco devices as well.

We will take a look at the various router command modes, set router passwords and banners, configure router hostnames and interface descriptions, and much more.

Overview of Router Modes

Once you login into a router you instantly enter the so-called user mode - the prompt [Router name] > appears. From this mode you can only see some statistic information.

To view and change the configuration of the router you have to enter into the privileged mode by entering the enable command. Here are the steps:




To be able to make global changes to the configuration of the router you have to enter the global configuration mode. Once you achieve that, you are able to access any possible subsequent configuration mode and make global changes:

RouterA#configure terminal or config t for short


Now you have the control of your device. If you need to modify your router's configuration then you enter the appropriate configuration mode. For example, if you want to make a change to your Fastethernet interface 0/0 then you have to enter interface configuration mode and make your modifications from there. Here are the steps:

RouterA(config)# interface fastethernet 0/0


Prompt RouterA(config-if)# indicates you are in interface configuration mode. At any time, and any mode you are in, you can insert a question mark ? and the router will automatically show all the possible commands or option parameters you can apply at that specific time.

RouterA(config-if)# ?

Interface configuration commands:access-expression Build a bridge boolean access expressionarp Set arp type (arpa, probe, snap) or timeout

backup Modify backup parameters

ip Interface Internet Protocol config commands .

Below there is a list of the most important configuration modes along with the commands used to enter these modes:

Name Your Router and Adjust its Clock

To apply an identity to your router, use the hostname command. To adjust the clock on the router use the clock set command. Always use the ? to help you correctly finish the command:

Setting Banners

It's a good idea to configure security notices to be displayed every time someone accesses your router. These notices are considered to be valid legal notices. The most useful banner is the so-called Message Of The Day (MOTD) banner.

This banner is displayed to every user connecting to the router either via telnet, console port or auxiliary port. This is how you can set it on your router:

RouterA(config)# banner motd ?

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