CCNA | Intro to the CLI | 4

Introduction to Cisco IOS CLI

  • Cisco IOS: Operating system for Cisco devices (routers, switches, firewalls).

  • Different from Apple's iOS.

  • CLI: Command Line Interface used for configuring devices.

  • GUI: Graphical User Interface, not covered in this course.

Connecting to a Cisco Device

  • Connect via console port:

    • Bring laptop to device.

    • Use either RJ45 port or USB Mini-B connector.

  • Required cable:

    • Rollover cable: RJ45 to DB9 connector for serial port.

    • Serial ports are becoming rare on modern laptops, often require USB adapter.

Accessing the CLI

  • Use a terminal emulator (e.g., PuTTY).

    • Select 'Serial' and then click 'Open' to connect.

  • Default settings for connection:

    • Baud rate: 9600 bps.

    • Data bits: 8.

    • Stop bits: 1.

    • Parity: None.

    • Flow control: None.

CLI Modes

User Exec Mode

  • Entry level mode, limited access.

  • Indicated by " > " after the host name.

Privileged Exec Mode

  • Accessed by using the command enable from User Exec mode.

  • Indicated by " # " after the host name.

  • More powerful commands available than in User Exec mode.

Packet Tracer

  • Cisco Packet Tracer: Network simulator useful for CCNA labs.

  • Limited compared to real devices.

Command Shortcuts

  • Use the ? to see available commands.

  • Use the Tab key for command auto-completion (e.g., typing e n followed by Tab completes to enable).

Global Configuration Mode

Entering Global Configuration Mode

  • Command: configure terminal (shortcut: conf t).

  • Change device configuration.

Setting Passwords

  • Secure Privileged Exec mode with a password.

  • Command: enable password <password>.

  • Passwords are case-sensitive.

Configuration Files

Running Config

  • Active configuration, modified in CLI.

  • Command to view: show running config.

Startup Config

  • Configuration loaded on device boot.

  • Command to view: show startup config.

Saving Configuration

  • Save running config to startup config:

    • write

    • write memory

    • copy running-config startup-config

  • View saved configuration using show startup config.

Security Considerations

Encrypting Passwords

  • Command: service password encryption encrypts passwords in running config.

  • Number '7' indicates type of encryption used.

Using Enable Secret

  • Use enable secret <password> for a more secure encrypted password (indicated by number '5').

  • If both commands are issued, enable password will be ignored in favor of enable secret.

Deleting Commands

  • To remove a command, prefix with no, e.g., no service password encryption.

Summary of Commands

  • User Exec Mode:

    • enable : Shift to Privileged Exec mode.

  • Privileged Exec Mode:

    • configure terminal : Shift to Global Configuration mode.

    • enable password <password> : Set password for Privileged Exec mode.

    • show running config : View current active configuration.

    • Use write, write memory, or copy running-config startup-config to save configuration.