# Cisco CLI

There are various types of Cisco [Networking devices](https://app.gitbook.com/@mudassirs46/s/network-fundamentals/~/drafts/-MRZ8l67L5MHnaQIEh9W/types-of-networking-devices) used to connect different Networks using Cisco OS & CLI.

* Just like Windows OS which is the brain of the device where it is installed, Cisco's Operating System (OS) is 'Internet Operating System (IOS) which controls the Logic & Functions of Networking devices.  &#x20;
* And Just like Windows OS provides Command Prompt (CMD) which is a text based Interface where a user types the command & upon pressing the enter key it commands the Logic of that device which tells the device what to do, Command Line Interface (CLI) also does the same work.
* In return the Networking devices send a reply messages in CLI displaying the results.
* **Cisco CLI can be accessed in 3 ways:**
  1. [Console Port](https://app.gitbook.com/@mudassirs46/s/network-fundamentals/~/drafts/-MRZ8l67L5MHnaQIEh9W/console-port),&#x20;
  2. [Telnet Access](https://app.gitbook.com/@mudassirs46/s/network-fundamentals/~/drafts/-MRZ8l67L5MHnaQIEh9W/telnet-access-teletype-network-p-no.-23),&#x20;
  3. [SSH Access](https://app.gitbook.com/@mudassirs46/s/network-fundamentals/~/drafts/-MRZ8l67L5MHnaQIEh9W/ssh-secure-shell-p-no.-22).
*   **Accessed CLI can be used in Three** [**CLI Modes**](https://app.gitbook.com/@mudassirs46/s/network-fundamentals/~/drafts/-MRZ8l67L5MHnaQIEh9W/cli-modes)**:**

    1\. User EXEC Mode/User Mode, 2. Enable Mode/Privileged Mode/Privileged EXEC mode, 3. Configure Terminal Mode.
* **CLI's different Modes can be** [**secured** ](https://app.gitbook.com/@mudassirs46/s/network-fundamentals/~/drafts/-MRZ8l67L5MHnaQIEh9W/securing-user-mode-and-privileged-mode)**in Two ways:**
  1. Using password only
  2. Using Username & Password
  3. Using External [Authentication Servers](https://app.gitbook.com/@mudassirs46/s/network-fundamentals/~/drafts/-MRZ8l67L5MHnaQIEh9W/aaa-authentication-authorization-and-accounting-server)

## Reference:

CCNA 200-301 OCG, Volume 1, Pg. 87-88 - Wendell Odom.
