IP addressing and subnetting form the foundation of modern network design and are essential for efficient address allocation and routing. Understanding CIDR notation, subnet masks, and address classes enables network engineers to segment networks, optimize IP space usage, and implement security boundaries. The shift from classful to classless addressing revolutionized the internet by preventing IP address exhaustion and reducing routing table sizes—mastering subnetting techniques like VLSM and supernetting is crucial for designing scalable, well-organized networks that balance performance, security, and resource conservation.
What This Cheat Sheet Covers
This topic spans 12 focused tables and 103 indexed concepts. Below is a complete table-by-table outline of this topic, spanning foundational concepts through advanced details.
Table 1: CIDR Notation and Prefix Lengths
CIDR notation is the language modern networks use to describe address ranges, and these terms are the vocabulary you'll read and write constantly. The whole system hinges on one idea — a prefix length that splits the 32 bits into network and host portions — from which everything else follows: the subnet mask, the network and broadcast addresses, and the usable host range in between.
| Concept | Example | Description |
|---|---|---|
192.168.1.0/24 | • IP address followed by slash and prefix length (number of network bits) • replaces classful addressing and enables flexible subnetting | |
/24 = 255.255.255.0/16 = 255.255.0.0 | • Number of bits set to 1 in the subnet mask • shorter prefix = larger network, longer prefix = smaller network | |
/30 for point-to-point/23 for 510 hosts | • Shorthand for subnet mask • /30 provides 4 addresses (2 usable), /23 merges two /24 blocks | |
10.5.16.0/20 | • First address in a subnet where all host bits are 0 • identifies the subnet itself and cannot be assigned to a device | |
192.168.1.255/24 | • Last address in a subnet where all host bits are 1 • packets sent here reach all hosts on that subnet |