Subnetworks and Subnetting

1. Overview

A subnetwork or subnet is a logical subdivision of an IP network.:1,16 The practice of dividing a network into two or more networks is called subnetting.

Computers that belong to a subnet are addressed with an identical most-significant bit-group in their IP addresses. This results in the logical division of an IP address into two fields, the network number or routing prefix and the rest field or host identifier. The rest field is an identifier for a specific host or network interface.

2. Description

2.1 Subnetwork

A subnetwork, or subnet, is a logical, visible subdivision of an IP network. The practice of dividing a network into two or more networks is called subnetting.

2.1.1 Mask

Mask divider network and host.

2.2 Why do we subnet

We use subnets to break down our networks for authorization. For example, School networks.

• Teacher Network(192.168.0.1/24): AD, Moderate Access to the Internet. 
• Student Network(192.168.10.0/20): Very Little Access to the Internet
• IT Network(192.168.5.0/24): WWW, DNS, Administration, Full Access to the Internet

2.3 Examples

2.3.1 Example 1

• How many users are you going to have on your networks

Teachers: 205, Students: 3000, IT: 105 + 50 devices.

• Find the Mask needed to accommodate the number of users

Teachers: /24 - Mask 255.255.255.0, 11111111.11111111.11111111.00000000

Students: /20 - Mask 255.255.240.0, 11111111.11111111.11110000.00000000

# 240
2 ** 7 + 2 ** 6 + 2 ** 5 + 2 ** 4

IT: /24 - Mask 255.255.255.0, 11111111.11111111.11111111.00000000

2.3.2 Example 2

The concept of subnetting the IPv4 address space 200.100.10.0/24, which contains 256 addresses, into two smaller address spaces, namely 200.100.10.0/25 and 200.100.10.128/25 with 128 addresses each.

3. Reference

https://en.wikipedia.org/wiki/Mask_(computing)

https://en.wikipedia.org/wiki/Subnetwork

https://www.youtube.com/watch?v=_R-R1qUVLxw