3.2 Subnetting Explained

Key Concepts

• Subnet Mask
• CIDR Notation
• Subnetting Process
• VLSM (Variable Length Subnet Masking)

Subnet Mask

A subnet mask is a 32-bit number used to divide an IP address into network and host portions. It helps in identifying which part of the IP address represents the network and which part represents the host. Common subnet masks include 255.255.255.0 (for a /24 network) and 255.255.0.0 (for a /16 network).

Example: Think of a subnet mask as a divider in a book. Just as a book is divided into chapters and sections, an IP address is divided into network and host parts using a subnet mask.

CIDR Notation

CIDR (Classless Inter-Domain Routing) notation is a compact representation of an IP address and its associated subnet mask. It is expressed as the IP address followed by a slash and the number of bits in the subnet mask (e.g., 192.168.1.0/24). CIDR notation simplifies the representation of IP networks and is widely used in modern networking.

Example: Consider CIDR notation as a shorthand for writing addresses. Just as "apt. 123" is a shorter way to write "apartment number 123," CIDR notation is a shorter way to represent an IP network and its subnet mask.

Subnetting Process

Subnetting is the process of dividing a network into smaller, more manageable subnetworks. This involves borrowing bits from the host portion of the IP address to create additional subnets. The number of subnets and hosts per subnet can be calculated using the formula 2^n (where n is the number of bits borrowed).

Example: Imagine subnetting as dividing a large pizza into smaller slices. Just as a pizza can be divided into 8 or 16 slices, a network can be divided into multiple subnets with each subnet having a specific number of hosts.

VLSM (Variable Length Subnet Masking)

VLSM is a technique used to create subnets of different sizes within the same network. This allows for more efficient use of IP addresses by allocating only the necessary number of addresses to each subnet. VLSM is particularly useful in large networks with varying host requirements.

Example: Think of VLSM as customizing the size of pizza slices. Just as you can have some slices larger and some smaller, VLSM allows you to create subnets with different numbers of hosts, optimizing the use of available IP addresses.