Module 2 (NetAcad)

Operating System (OS)

The software that manages hardware and provides an interface for the user.

Kernel

The core of the OS that interacts directly with hardware.

Shell

The user interface portion of the OS.

Command-Line Interface (CLI)

A text-based interface for interacting with an OS (e.g., Cisco IOS, Linux terminal).

Graphical User Interface (GUI)

A visual, icon-based interface (e.g., Windows, macOS).

Cisco IOS (Internetwork Operating System)

The network operating system used on most Cisco routers and switches.

Terminal Emulation Program

Software used to connect to a device's CLI (e.g., PuTTY, Tera Term, SecureCRT).

Console

An "out-of-band" physical connection for initial configuration.

SSH (Secure Shell) / Telnet

"In-band" methods for remote access over an active network. SSH is secure (encrypted); Telnet is not.

User EXEC Mode (> prompt)

Limited, view-only mode for basic monitoring.

Privileged EXEC Mode (# prompt)

Provides access to all monitoring commands and entry to configuration modes. Also called "enable mode."

Global Configuration Mode ((config)# prompt)

For device-wide configuration changes.

Line Configuration Mode ((config-line)# prompt)

For configuring console, SSH, Telnet, or AUX access.

Interface Configuration Mode ((config-if)# prompt)

For configuring a specific port or interface.

enable

Moves from User EXEC to Privileged EXEC mode.

configure terminal

Moves from Privileged EXEC to Global Config mode.

exit

Moves back one level in the mode hierarchy.

end or Ctrl+Z

Jumps from any sub-configuration mode back to Privileged EXEC mode.

Command Structure

command keyword argument (e.g., ping 192.168.1.1).

Context-Sensitive Help (?)

Shows available commands or options.

Hot Keys & Shortcuts

Tab for command completion, Ctrl+C to abort a command.

Hostname

A unique, descriptive name for a device.

line console 0

Secures User EXEC access via the console port.

line vty 0 15

Secures remote access via Telnet/SSH.

enable secret

Secures Privileged EXEC mode access (this password is encrypted by default).

service password-encryption

A command that applies weak encryption to all plaintext passwords in the configuration file.

banner motd #…#

Creates a "Message of the Day" banner for legal warnings.

running-config

The current, active configuration stored in RAM (volatile). Changes here take effect immediately.

startup-config

The saved configuration stored in NVRAM (non-volatile). This is the file loaded when the device boots up.

Saving Configurations

The copy running-config startup-config command saves your current changes.

IP Address

A unique logical address used for communication across networks.

IPv4

32-bit address (e.g., 192.168.1.10).

IPv6

128-bit address (e.g., 2001

Subnet Mask

Used with an IPv4 address to distinguish the network portion from the host portion.

Default Gateway

The IP address of the router on the local network that a device uses to reach remote networks.

DHCP (Dynamic Host Configuration Protocol)

A service that automatically assigns IP address information to devices.

SVI (Switch Virtual Interface)

A logical interface on a switch that can be assigned an IP address to allow for remote management of the switch. The default is interface vlan 1.

ipconfig (on Windows PC)

Displays the IP configuration of the PC.

ping

Tests basic end-to-end connectivity between two devices.

show running-config

Displays the current configuration file.

show ip interface brief

Shows a summary of the status of a device's interfaces.