CCNA 200-301 Cheat Sheet: 1.0 Network Fundamentals (20%)

Story time: I recently landed an interview with one of the companies I’ve been aiming to work for. The technical discussion centered around CCNA-level knowledge, which made me realize it’s time for a refresher. It’s been a while since I passed the CCNA exam, and as they say—if you don’t use it, you lose it. So, this week, I’m kicking off a CCNA review series to sharpen my skills and share what I’ve learned along the way.

The Network Fundamentals domain of the CCNA 200-301 exam is all about the building blocks of modern computer networks. Whether you’re preparing for the certification or getting hands-on in the field, a solid understanding of how devices connect, communicate, and operate at the most basic level is essential.

This detailed guide will help you grasp the core concepts covered in the 1.0 exam section and serves as a foundational reference for your study or review.

1.1 Role and Function of Network Components

Understanding the function of each network device is crucial. These devices are the physical and logical tools that shape how networks operate.

Routers: Direct data packets between different IP networks. Operate at Layer 3 (Network Layer) of the OSI model.
Switches: Connect devices within the same local network. Operate primarily at Layer 2 (Data Link), forwarding frames based on MAC addresses.
Firewalls: Monitor and filter incoming/outgoing traffic based on defined security rules. They can be standalone or integrated into routers.
Access Points (APs): Extend wireless coverage and connect wireless devices to a wired LAN.
Controllers (WLCs): Manage multiple access points centrally, ideal for enterprise wireless networks.
Endpoints: End-user devices like PCs, phones, or printers that consume or generate network traffic.
Servers: Provide network resources like websites, files, applications, or email.
Power over Ethernet (PoE): Supplies power to devices like IP cameras and APs through the Ethernet cable, removing the need for separate power sources.

1.2 Network Topology Architectures

Network topology defines how devices and connections are arranged. It affects performance, scalability, and fault tolerance.

Two-tier architecture: Combines core and access layers. Suitable for small to medium-sized networks.
Three-tier architecture: Adds a distribution layer between core and access layers, offering more scalability and segmentation.
Spine-leaf: Common in data centers. All leaf switches connect to all spine switches, providing high bandwidth and minimal latency.
WAN (Wide Area Network): Connects remote sites over long distances using leased lines, VPNs, or internet.
SOHO (Small Office/Home Office): A compact network combining routing, switching, and wireless in one device.
On-premises vs. Cloud: On-prem infrastructure is locally hosted and managed. Cloud services are externally hosted and accessed over the internet.

1.3 Physical Interfaces and Cabling

The physical medium through which devices communicate affects speed, reliability, and distance.

Fiber Optic Cables:
- Single-mode fiber (SMF): Long-distance communication using a single light path; used in ISPs and data centers.
- Multi-mode fiber (MMF): Short-distance communication with wider cores; often used within buildings.
Copper Cables:
- Twisted-pair (Cat5e, Cat6, Cat6a): Common in Ethernet networks, suitable for short to moderate distances.
Common Connectors:
- RJ45: Used with Ethernet copper cables.
- SFP (Small Form-factor Pluggable): Interface for fiber and high-speed copper transceivers.

1.4 Interface and Cable Issues

Misconfigured or faulty physical interfaces can cause serious connectivity problems.

Collisions: Occur when two devices transmit simultaneously. Rare in full-duplex switched environments.
CRC Errors: Indicate corrupted frames due to poor cabling or interference.
Duplex Mismatch: One side is full-duplex, the other is half; causes performance degradation.
Speed Mismatch: If connected devices have differing speed settings, the link may fail to establish.

1.5 TCP vs. UDP

Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) are two key transport layer protocols, each serving different needs.

TCP:
- Reliable, connection-oriented.
- Guarantees packet delivery through acknowledgments, retransmissions, and sequencing.
- Used for applications like web browsing (HTTP/HTTPS), email, and file transfers.
UDP:
- Unreliable, connectionless.
- Faster, with less overhead.
- Used in latency-sensitive applications like voice (VoIP), video streaming, and DNS queries.

1.6 IPv4 Addressing and Subnetting

IPv4 is the most widely used IP addressing format. Subnetting is the process of dividing a network into smaller segments.

IPv4 Format: 32-bit addresses written as four decimal numbers (e.g., 192.168.1.1).
Subnet Mask: Defines how many bits belong to the network vs. host (e.g., 255.255.255.0 = /24).
CIDR Notation: Uses slash (/) to indicate subnet size (e.g., /24 means 256 IPs with 254 usable).

Basic subnetting knowledge includes:

Calculating number of subnets or hosts.
Identifying network, broadcast, and usable IP ranges.

1.7 Private IPv4 Addressing

Per RFC1918, these addresses are reserved for private use within networks and are not routable on the public internet.

Class	Private IP Range
A	10.0.0.0 – 10.255.255.255
B	172.16.0.0 – 172.31.255.255
C	192.168.0.0 – 192.168.255.255

Private IPs are typically translated to public IPs using NAT (Network Address Translation).

1.8 IPv6 Addressing and Prefix

IPv6 was developed to address IPv4 exhaustion, offering a vastly larger address space.

Format: 128-bit hexadecimal, e.g., 2001:0db8:85a3::8a2e:0370:7334.
Prefix Length: Equivalent of subnet mask, written as /64, /128, etc.
IPv6 supports auto-configuration using:
- Stateless (SLAAC): No server required.
- Stateful (DHCPv6): Uses a DHCP server.

1.9 IPv6 Address Types

Unicast: A single, unique destination address.
Multicast: One-to-many communication (e.g., all routers: FF02::2).
Anycast: One-to-nearest communication; all devices share the same address, but packets are routed to the closest one.
EUI-64: Extends the interface ID using the device’s MAC address for stateless configuration.

1.10 IP Parameter Verification for Client OS

Being able to verify IP settings on different operating systems is critical for troubleshooting.

Windows: ipconfig /all – Shows all IP configuration details.
Linux/macOS: ifconfig or ip a – Display current network configuration.

Parameters to verify:

IP address
Subnet mask
Default gateway
DNS servers

1.11 Wireless Principles

Wireless networking fundamentals focus on how data is transmitted over the air.

SSID (Service Set Identifier): The name of the wireless network.
Frequency Bands:
- 2.4 GHz: Longer range, more interference, fewer non-overlapping channels (1, 6, 11).
- 5 GHz: Shorter range, more channels, less interference.
Encryption Standards:
- WEP: Outdated and insecure.
- WPA2/WPA3: Current standards for secure wireless communication.
RF Behavior: Signal strength, interference, and channel overlap affect connectivity.

1.12 Virtualization Fundamentals

Virtualization allows multiple operating systems or services to run on a single physical device.

Virtual Machines (VMs): Run full operating systems inside a host machine via hypervisors like VMware or Hyper-V.
Containers: Lightweight, share the host OS kernel. Examples include Docker.
VRF (Virtual Routing and Forwarding): Multiple routing tables on the same router, enabling network segmentation.

1.13 Switching Concepts

Switches play a critical role in forwarding traffic within LANs by learning device MAC addresses.

MAC Learning: Switch maps source MAC addresses to specific ports.
Forwarding: If the destination MAC is known, the frame is sent to that port only.
Flooding: If the destination MAC is unknown, the frame is sent out all ports (except incoming).
MAC Table: Also called CAM (Content Addressable Memory) table; it dynamically stores learned MAC addresses and associated ports.

Finally…

The 1.0 Network Fundamentals section provides the core concepts every network engineer must understand. These principles underpin everything from advanced routing to network automation. If you’re studying for the CCNA or working on improving your foundational knowledge, master these topics first—they will help you succeed in both exams and real-world scenarios.