Kable Academy — Interactive Subnetting Guide

01 · WHAT IS SUBNETTING?

A subnet (subnetwork) is a logical subdivision of a larger IP network. Subnetting lets you take one big network and slice it into smaller, more manageable pieces — each one acting as its own isolated segment.

Think of it like an office building: the building has one street address (your network address), but inside there are separate floors and rooms — each with its own internal structure. Routers act as the security desks between floors.

WHY SUBNET?

Security isolation

Separate departments (HR, Finance, IT) so a breach in one segment cannot spread to others without crossing a firewall or router.

Reduced broadcast traffic

Broadcasts only reach devices in the same subnet, dramatically cutting down noise on large networks.

Efficient IP use

Allocate exactly as many addresses as a segment needs instead of wasting a whole Class A (16 million addresses!) on a 50-host office.

Easier routing

Routers can summarize many subnets into one route entry, keeping routing tables small and lookups fast.

KEY TERMINOLOGY

Term	Definition
Network address	The first address in a subnet — identifies the subnet itself. Never assigned to a host.
Broadcast address	The last address in a subnet — sends data to ALL hosts in that subnet. Never assigned to a host.
Host range	All addresses between network and broadcast — these are the usable addresses assigned to devices.
Subnet mask	32-bit number showing which bits are the network portion vs the host portion. E.g. 255.255.255.0
CIDR notation	Shorthand for the prefix length after a slash: /24 means 24 bits are the network, 8 bits are hosts.
Default gateway	The router interface IP that connects this subnet to other networks or the internet.
Usable hosts	Formula: 2^(host bits) − 2. The −2 removes the network and broadcast addresses. /24 → 254 usable.
Wildcard mask	The inverse of the subnet mask. Used in router ACLs and OSPF. /24 → 0.0.0.255

HOW A SUBNET MASK WORKS

A subnet mask is a 32-bit number that tells a device which part of an IP address is the network and which part identifies individual hosts. 1-bits mark the network portion; 0-bits mark the host portion.

IP address: 192.168.1.42 Subnet mask: 255.255.255.0 CIDR notation: 192.168.1.42/24 Network part: 192.168.1.x (first 24 bits — fixed for all hosts in subnet) Host part: .0 to .255 (last 8 bits — unique per device) Usable hosts: .1 to .254 (256 total − 2 = 254)

The /24 in CIDR notation means the first 24 bits are the network. That leaves 8 bits for hosts — giving 2⁸ = 256 total addresses, with 254 usable ones.

02 · IPv4 ADDRESS CLASSES

Before CIDR, addresses were grouped into fixed classes A, B, and C — each with a different split between network and host bits. Understanding classes helps you recognize default masks instantly.

LIVE CLASS DETECTOR

Type any IP address — instantly identify its class, default mask, and usable host count:

IP ADDRESS

PRIVATE ADDRESS RANGES (RFC 1918)

These ranges are reserved for internal networks and are never routed on the public internet:

CIDR PREFIX QUICK REFERENCE

CIDR	Subnet mask	Usable hosts	Subnets from /24	Common use

03 · SUBNET CALCULATOR

Enter any IP address and CIDR prefix to get the complete subnet breakdown instantly:

NETWORK ADDRESS (IP)

CIDR PREFIX LENGTH

SUBNETTING PLANNER

Enter your base network and how many subnets you need — find the right prefix automatically:

BASE NETWORK ADDRESS

BASE PREFIX

SUBNETS NEEDED

04 · BINARY BIT VISUALIZER

See exactly how a subnet mask divides an IP address bit-by-bit into network, subnet, and host portions:

IP ADDRESS

CIDR PREFIX

Network bits

Subnet bits

Host bits

SUBNET BLOCK VISUALIZER

See how subnets divide up a /24 address space into equal blocks:

BASE /24 NETWORK

SUBNET PREFIX

SUBNETTING CHEAT SHEET — POWERS OF 2

Host bits (n)	2^n total	Usable hosts	Prefix	Block size
1	2	0	/31 (P2P)	2
2	4	2	/30	4
3	8	6	/29	8
4	16	14	/28	16
5	32	30	/27	32
6	64	62	/26	64
7	128	126	/25	128
8	256	254	/24	256
16	65,536	65,534	/16	65,536
24	16,777,216	16,777,214	/8	16,777,216

05 · PRACTICE QUIZ

Question 1 of 10

Difficulty:

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