Cisco IOS Basic Commands

Cisco IOS, which stands for Internetwork Operating System, is the proprietary multitasking operating system that runs on the vast majority of Cisco Systems routers and network switches.

Just like Microsoft Windows or macOS manages your computer’s hardware and software applications, Cisco IOS manages the routing, switching, telecommunications, and security functions of enterprise network devices.

What Does Cisco IOS Actually Do?

Cisco IOS acts as the bridge between the physical hardware (ports, memory, ASICs) and the network protocols required to move data across the globe. Its primary responsibilities include:

• Routing and Switching: Directing data packets along the most efficient paths using protocols like OSPF, EIGRP, and BGP.
• Security & Access Control: Managing firewalls, encryption, and Access Control Lists (ACLs) to prevent unauthorized network entry.
• Network Scalability: Supporting advanced features like Virtual Local Area Networks (VLANs), Quality of Service (QoS) traffic prioritizing, and Network Address Translation (NAT).
• Device Management: Allowing network administrators to configure, monitor, and troubleshoot the hardware remotely or via a physical console cable.

Cisco IOS Command Line Interface

Unlike consumer routers (like the one in your home) that use a visual web browser interface, Cisco IOS is primarily managed using a text-based Command Line Interface (CLI).

Because routers and switches don’t usually have monitors attached to them, network engineers connect to Cisco IOS using a laptop via a Console Cable, or remotely using secure network protocols like SSH (Secure Shell).

Cisco IOS Command Line Structure

To prevent accidental changes to a live network, Cisco IOS organizes its interface into hierarchical modes. You must navigate through these modes depending on what you want to achieve. Basically, it has three main modes:

• User EXEC Mode
• Privileged EXEC Mode (Enable Mode)
• Global Configuration Mode

1. User EXEC Mode

This is the default mode you land in when you first connect to a Cisco device. It is a “read-only” environment designed for basic inspection.

• Prompt: Router> (or Switch>)
• Privilege Level: Lowest. You cannot change any settings or view sensitive configuration files.
• Common Commands:
  • >ping
  • >traceroute
  • >show version
• How to exit: Type logout or exit.

2. Privileged EXEC Mode (Enable Mode)

Also known as “Enable Mode,” this is the administrative and diagnostic hub of the device. You usually have to enter a password to get here.

• Prompt: Router# (or Switch#)
• Privilege Level: High. You can view the entire device configuration, restart the system, back up settings, and run detailed troubleshooting commands.
• How to enter: From User EXEC, type enable.
• Common Commands:
  • #show running-config
  • #copy running-config
  • #startup-config
  • #reload.
• How to exit: Type disable to go back to User EXEC, or exit to disconnect.

3. Global Configuration Mode

If you want to make a change that affects the entire device (like changing its name or setting up security banners), you must enter Global Configuration Mode.

• Prompt: Router(config)#
• Privilege Level: Modification level. Changes made here take effect immediately in the device’s active memory.
• How to enter: From Privileged EXEC, type configure terminal (or the shortcut conf t).
• Common Commands:
  • (config)#hostname <name of router>
  • (config)#enable secret <secret password>
  • (config)#banner motd <message that is to be displayed after the initial booting of the router>.
• How to exit: Type exit to go back to Privileged EXEC, or press Ctrl+Z (or type end) to jump straight back to Privileged EXEC from any deeper config mode.

4. Sub-Configuration Modes

From Global Configuration mode, you can dive deeper into specific components of the router or switch. The two most common sub-modes are:

A. Interface Configuration Mode

Used to configure specific physical ports (like GigabitEthernet 0/1) or virtual interfaces.

• Prompt: Router(config-if)#
• How to enter: From Global Config, type interface [interface-name] (e.g., interface gigabitethernet 0/0).
• Common Commands:
  • (config-if)#ip address <ip address> <subnet mask>
  • (config-if)#no shutdown
  • (config-if)#description.

B. Line Configuration Mode

Used to configure access paths to the device, such as the physical Console port or virtual terminal lines (VTY) used for remote Telnet/SSH access.

• Prompt: Router(config-line)#
• How to enter: From Global Config, type line console 0 or line vty 0 4.
• Common Commands:
  • (config-line)#password <log in password>
  • (config-line)#login

---

Cisco IOS Basic Commands Summary

Mode	CLI Command	Description
User EXEC (>)	enable	Access Privileged EXEC Mode.
User EXEC (>)	configure terminal	Enter Global Configuration Mode (Note: Usually executed from Privileged EXEC, but included here for workflow continuity).
Privileged EXEC (#)	disable	Return to User EXEC Mode.
Privileged EXEC (#)	show ip interface brief	View brief status and IP addresses for all interfaces.
Privileged EXEC (#)	show running-config	Display the current active configuration in RAM.
Global Configuration ((config)#)	interface <id>	Select a specific interface to configure (e.g., interface gigabitethernet0/1).
Global Configuration ((config)#)	hostname <name>	Assign a unique device name to the switch or router.
Interface Configuration ((config-if)#)	ip address <ip> <mask>	Configure the IPv4 address and subnet mask on the interface.
Interface Configuration ((config-if)#)	no shutdown	Administratively enable the interface (turns it on).
Interface Configuration ((config-if)#)	description <text>	Add a helpful descriptive label to the interface for documentation.