Master IP Addressing: From Basics to Subnetting and VLSM Explained

IP Address Format

IP address is a 32‑bit binary identifier that uniquely identifies a device on a network.

Features

Uniqueness : each address identifies one device at a time.

Structure : composed of a network part and a host part.

IP Address Classification

Components

Four octets, each ranging from 0 to 255, divided into network and host portions.

Network part : identifies the subnet.

Host part : identifies the host within the subnet.

Classes

Class A, B, C, D, E with default masks.

Class A: 0‑127, network 8 bits, default mask 255.0.0.0 Class B: 128‑191, network 16 bits, default mask 255.255.0.0 Class C: 192‑223, network 24 bits, default mask

255.255.255.0

Private IP Ranges

10.0.0.0/8 (Class A)

172.16.0.0‑172.31.255.255 (Class B)

192.168.0.0‑192.168.255.255 (Class C)

Subnet Mask

Subnet mask determines the network portion; bits set to 1 represent the network, bits set to 0 represent the host.

Logical AND between IP address and subnet mask yields the network address.

AND rule : 0 AND any = 0; 1 AND any = the other bit.

Binary and Decimal

Binary

Base 2, digits 0 and 1.

Conversion using positional values (2ⁿ).

Example:

159.64.25.100 = 10011111.01000000.00011001.01100100

Decimal

Base 10, digits 0‑9.

Conversion using the remainder method (divide by 2, record remainders).

IP Address Planning

Reasons for Subnetting

Meet different network size requirements.

Provide hierarchical network structure.

Conserve address space.

Subnetting Principles

Based on classful or classless (CIDR) addressing.

Determine number of subnets and hosts per subnet.

Apply soft rules (administrative convenience) and hard rules (technical limits).

Soft Rules Example

Assigning whole floors of a building to separate /24 subnets, e.g., 192.168.10.0/24 for floor 10.

Hard Rules Example

Analyze departmental host counts, decide required subnets, calculate needed IP counts and masks.

VLSM (Variable Length Subnet Mask)

VLSM allows different mask lengths for each subnet, improving address utilization and routing efficiency.

Advantages : higher utilization, greater flexibility, more efficient routing.

Implementation Steps :

Determine subnet requirements (host count per subnet).

Calculate appropriate subnet masks.

Divide the network into subnets accordingly.

Assign IP address blocks to each subnet.

Example : Split 192.168.1.0/24 into four subnets for 50, 20, 10, and 5 hosts.

Subnet 1: /26 (255.255.255.192) → 192.168.1.0‑192.168.1.63

Subnet 2: /27 (255.255.255.224) → 192.168.1.64‑192.168.1.95

Subnet 3: /28 (255.255.255.240) → 192.168.1.96‑192.168.1.111

Subnet 4: /29 (255.255.255.248) → 192.168.1.112‑192.168.1.119

Summary

IP address format and classification, including private ranges and default masks.

Binary‑decimal conversion methods for IP addresses.

Subnet mask purpose and AND operation to obtain network addresses.

Reasons and principles behind subnetting, with hard and soft rules.

VLSM benefits, step‑by‑step implementation, and a practical example.

Key planning principles: uniqueness, scalability, continuity, and meaningful allocation.