What is Cisco IOS commands?

We’re going to use Cisco Packet Tracer App from Cisco NetAcad dot com to configure a Cisco 1841 Router.

Learning-by-doing, that’s my motto!

This post aims to introduce a new Cisco Internetworking (IOS) operating system for the command line user IOS Interface (CLI).

After reading this post, a user will understand how to operate the IOS CLI to configure and manage an IOS Cisco router.

Packet Tracer is a tool that allows you to simulate real networks.

It provides three main menus that allow you to:

Here are some Cisco terms to help you understand this theme as you read this post:

A Cisco IOS router command line interface can be accessed through a console or connection, modem connection, or a telnet/ssh session.

Regardless of which connection method is used, access to the IOS command-line interface is generally referred to as an EXEC session.

As a security feature, Cisco IOS separates EXEC sessions into two different access levels — the user level and the privileged EXEC level.

EXEC user level allows a person to access only a limited amount of basic monitoring commands.

Privileged EXEC level allows a person to access all of the router’s commands (eg, configuration and management) and can be password protected to allow only authorized users the ability to configure or maintain the router.

Once an EXEC session is established, commands within Cisco IOS are hierarchically structured. In order to be able to configure the router, it is important to understand this hierarchy.

To illustrate this hierarchy, Fig. 1 presents a simple high-level schematic diagram of some IOS commands:

For example, when an EXEC session is started, the router will show a Router> prompt.

The right arrow (>) at the prompt indicates that the router is at the EXEC user level.

The EXEC user level does not contain all commands that can control (for example, reload or configure) the operation of the router.

To list the commands available at the EXEC user level, type a question mark (?) At the Router> prompt. (This feature is called context-sensitive help.)

Critical commands (for example, configuration, and management) require the user to be at the privileged EXEC level.

To switch to the privileged EXEC level, type enable at the Router> prompt.

If an activation password is configured, the router will then ask for the password.

When the correct activation password is entered, the prompt router will change to Router #, indicating that the user is now at the privileged EXEC level.

To return to the EXEC user level, type disables at the Router # prompt.

Entering a question mark (?) in the privileged EXEC level will now reveal many more command options than are available at the EXEC user level.

The basic CLI modes that we will be referring to below are as follows:

Note: For security reasons, the router will not echo the password that is entered. Also, be aware that if you configure a router via telnet, the password is sent in cleartext :/

Telnet does not offer a method for protecting packets. Once an EXEC session is established, commands within Cisco IOS are hierarchically structured. In order to be able to configure the router, it is important to understand this hierarchy.

The configuration command options will not be available until the user has navigated to the configuration branch of the IOS CLI structure.

Once in the configuration branch, a user can enter the configuration system-level commands that apply to the entire router at the global configuration level.

Specific interface configuration commands are available once the user has switched to the particular interface configuration level.

More detailed information and examples of how to navigate the IOS CLI hierarchy are offered on the 1841 router configuration specification Cisco’s page.

To assist users in navigating through IOS CLI, the command prompt will be changed to reflect a user’s position within the command hierarchy.

This allows users to easily identify where within the command structure they are at any given time.

Cisco Packet Tracer

Let’s practice now:

Go to Cisco Network academy and download the Cisco Packet Tracer application, if you have not done so already :)

You will need to register on the Cisco website first.

When you ready, download the CCLAB_01.pkt file and click it.

A new session of Cisco Packet Tracer will open \o/

The Basic Configuration of Cisco Routers:

# Step — The CCLAB_01.pkt file is properly configured.

Open this file at Cisco Packet Tracer (mine is v. 7.3.1.0362).

Right-click the 1841 Router in your topology.

Go to the CLI tab.

Hit enter, and you are ready to go!

Let’s begging by deleting all settings using the commands below:

Now go to the Physical tab and turn off the router and immediately turn it on again.

The system will reboot and will load the original basic Cisco 1884 router configuration.

Return to the CLI tab and you will see the boot process running right away.

Fine!

# Step — Now this message appears (choose no):

We will use a manual configuration.

So far, so good!

# Step — Now follows this table sequence:

# Step —To test remote access to the router use the PC-PT 192.168.0.1 Address Machine on your network, by typing this address 192.168.0.254 via the Telnet application.

To exit, type exit ;)

See, Telnet is not a recommended protocol. It transports data in a clear text (Port 23).

The Telnet protocol can be used by an attacker to gain remote access to a Cisco network switch. In an earlier topic, you configured a login password for the vty lines and set the lines to require password authentication to gain access.

In the next step, I explain how to use the SSH protocol (port 23).

Be aware that Cisco Packet Tracer does not support SSH :/

# Step — Roadmap for configuring the SSH protocol on remote access:

That’s it!.

Congrats! You now are Cisco Technician!

SSH v2 is enabled! Your router will now be accessible on Port 22, and no longer on Port 23, Telnet.

Again, the Cisco Packet Tracer does not support SSH, but the message was given, right?

See you in the next Cisco Episode where we will see the static routing.

Be tuned o/

Bye!

Download All Files For This Project

Notes:

TTL means “time to live”. It is a value on an ICMP packet that prevents that packet from propagating back and forth between hosts ad infinitum. Each router that touches the packet decrements the TTL. If the TTL ever reaches zero, the packet is discarded. It’s also a measure of how many hops the packet took.

Since Packet Tracer simulates networks and network traffic, the physical aspects of these networks also need to be simulated.

This includes actually finding and deploying physical devices, customizing those devices, and cabling those devices.

After the physical deployment and cabling are done, then it is time for the configuration of the interfaces used to connect the devices.

Why no ip domain lookup?

Credits & References

Laboratorios de Tecnologias Cisco em Infraestrutura de Redes by Samuel H. B. Brito

The purpose of the DTE and the DCE in the Cisco CCNA by danscourses

Internet service provider by Wikipedia

Colocation centre by Wikipedia

Learning-by-doing by Wikipedia

Cisco Product Documentation https://docstore.mik.ua/univercd/cc/td/doc/product/index.html

Cisco CCNA 200–301 Exam: Complete Course with practical labs by David Bombal from Udemy — The complete course to help you prepare and pass Cisco’s newest CCNA 200–301 exam. Everything you need: Theory and labs

Edited: ago,2022 <no ip domain lookup explainned :)>