4-2-2 Subnetting Explained

Key Concepts

• IP Addressing
• Subnet Mask
• CIDR Notation
• Subnetting Process
• Subnet Calculation

IP Addressing

An IP address is a unique identifier assigned to each device on a network. It consists of a network portion and a host portion. For example, in the IP address 192.168.1.1, the first three octets (192.168.1) represent the network, and the last octet (1) represents the host.

Subnet Mask

A subnet mask is used to divide an IP address into network and host portions. It is a 32-bit number that masks the IP address, separating it into network address and host address. For example, the subnet mask 255.255.255.0 indicates that the first 24 bits are the network portion, and the last 8 bits are the host portion.

CIDR Notation

CIDR (Classless Inter-Domain Routing) notation is a compact representation of an IP address and its associated network mask. It is written as the IP address followed by a slash and the number of bits in the subnet mask. For example, 192.168.1.0/24 represents a network with a 24-bit subnet mask.

Subnetting Process

Subnetting involves dividing a network into smaller, more manageable subnetworks. The process includes:

1. Determining the number of subnets needed.
2. Calculating the new subnet mask.
3. Assigning IP addresses to each subnet.
4. Ensuring proper routing between subnets.

Subnet Calculation

To calculate subnets, follow these steps:

1. Determine the number of bits needed for the subnet mask. For example, to create 4 subnets, you need 2 additional bits (2^2 = 4).
2. Extend the subnet mask by the number of bits determined. For a /24 network, extending by 2 bits results in a /26 subnet mask.
3. Calculate the number of hosts per subnet. For a /26 subnet, there are 64 addresses (2^(32-26) = 64), with 62 usable hosts (64 - 2 for network and broadcast addresses).
4. Assign IP ranges to each subnet. For example, the first subnet could use 192.168.1.0/26, the second 192.168.1.64/26, and so on.

Examples and Analogies

Think of an IP address as a house address, with the network portion being the street name and the host portion being the house number. Subnetting is like dividing a street into smaller blocks, each with its own set of house numbers.

CIDR notation is like a shorthand for describing the size of each block. For example, /24 is like saying a block has 256 houses, while /26 means each block has 64 houses.

Subnetting allows network administrators to manage larger networks more efficiently, similar to how city planners manage neighborhoods by dividing them into smaller, more manageable sections.