11 - CCNA 1 Cheat Sheet with Examples

Use this CCNA 1 cheat sheet to review core networking concepts and common Cisco IOS commands. The examples use documentation addresses and a lab switch; adapt interface names and addresses to your own authorized lab.

Network basics

• Host: A device that sends or receives network traffic.
• Switch: Forwards Ethernet frames within a local network, using MAC addresses.
• Router: Forwards packets between IP networks, using IP addresses and a routing table.
• LAN: A local area network, usually covering a limited area.
• WAN: A wide area network connecting networks across larger distances.
• Default gateway: The local router address a host uses to reach other networks.
• Encapsulation: Each networking layer adds information needed to deliver data.

OSI model

Layer	Name	Example
7	Application	HTTP, DNS
6	Presentation	Data format and encryption
5	Session	Manages communication sessions
4	Transport	TCP, UDP
3	Network	IP addressing and routing
2	Data Link	Ethernet frames and MAC addresses
1	Physical	Cables, fiber, and signals

When troubleshooting, move from physical connectivity upward: check the link, local network settings, routing, and then the application.

IPv4 address and subnet example

An IPv4 address is 32 bits, usually written as four decimal octets. A prefix length identifies the network portion.

Example: 192.0.2.25/24

• Subnet mask: 255.255.255.0
• Network address: 192.0.2.0
• Usable host range: 192.0.2.1–192.0.2.254
• Broadcast address: 192.0.2.255

For a /24, the first 24 bits are the network portion and the last 8 bits are for host addresses. The first address identifies the subnet and the last is its broadcast address, so neither is assigned to a typical host.

Common prefix reference

Prefix	Subnet mask	Total addresses	Typical usable hosts
/24	255.255.255.0	256	254
/25	255.255.255.128	128	126
/26	255.255.255.192	64	62
/27	255.255.255.224	32	30
/30	255.255.255.252	4	2

These usable-host counts assume a traditional IPv4 subnet where the network and broadcast addresses are reserved.

Private IPv4 ranges

These address ranges are reserved for private networks and are not routed on the public internet:

• 10.0.0.0/8
• 172.16.0.0/12
• 192.168.0.0/16

Use the addresses assigned to your lab or network. An IP address, subnet mask, and default gateway must be appropriate for the network where the device is connected.

Common protocols and ports

Protocol	Default port	Purpose
FTP	TCP 20/21	File transfer; not encrypted by default
SSH	TCP 22	Secure remote command-line access
Telnet	TCP 23	Remote command-line access; not encrypted
DHCP	UDP 67/68	Automatically assigns IP configuration
DNS	UDP/TCP 53	Resolves names to IP addresses
HTTP	TCP 80	Web traffic
HTTPS	TCP 443	Encrypted web traffic
TFTP	UDP 69	Simple file transfer; not encrypted

Ports are defaults; services may be configured to use different ports.

Cisco IOS command modes

Prompt example	Mode	Common use
Switch>	User EXEC	Basic inspection
Switch#	Privileged EXEC	Verification and device management
Switch(config)#	Global configuration	Device-wide settings
Switch(config-if)#	Interface configuration	Configure a specific interface

Use enable to enter privileged EXEC mode, configure terminal to enter global configuration mode, exit to go back one level, and end to return to privileged EXEC mode.

Basic switch configuration example

This example labels a port and enables it. Interface names vary by model:

enable
configure terminal
hostname Switch1
interface GigabitEthernet0/1
description Connected-device
no shutdown
end
show interface status

On a Layer 2 switch, a management IP is commonly configured on a VLAN interface, and ip default-gateway points to the router on that management subnet. Use values and VLANs assigned for your lab.

configure terminal
interface vlan 1
ip address 192.0.2.10 255.255.255.0
no shutdown
exit
ip default-gateway 192.0.2.1
end
copy running-config startup-config

Useful verification commands

Run these from privileged EXEC mode (#):

Command	What it helps check
show running-config	Active configuration
show startup-config	Saved configuration
show ip interface brief	Interface IP addresses and status
show interfaces	Interface details and counters
show mac address-table	MAC addresses learned by a switch
show version	Device and software information
ping 192.0.2.1	Basic reachability to an IP address
traceroute 198.51.100.10	Path toward a destination, where supported

If a command is not available, use ? to see options for the current device and command mode. Output and support can differ across platforms.

Quick troubleshooting checklist

1. Check power, cables, and link/interface status.
2. Confirm the IP address and subnet mask on each device.
3. Check that devices on the same subnet have compatible addressing.
4. For a remote destination, verify the default gateway and routing.
5. Use ping and relevant show commands to narrow down where communication stops.
6. Change one setting at a time, then test again.

Save and back up configurations

Save the current running configuration to startup configuration when you are ready to keep your changes:

copy running-config startup-config

In a private lab, you can also copy a configuration to or from a TFTP server. TFTP does not encrypt data, so do not use it over an untrusted network or expose configuration files containing sensitive settings.

Related posts

Cisco CCNA1 Introduction and Switch and Router Modes

CCNA 1 Tips and Tricks for Beginners

Set a Default Gateway on a Cisco Switch

Configure a Port on a Cisco Switch

Save a Cisco Configuration to a TFTP Server