# Day 40 – Subnetting

• must be in the form of A.B.C.D,
• where A, B, C, and D are numbers from 0-255
• The numbers cannot be 0 prefixed unless they are 0.

Subnetting – the process of taking a large network and splitting it up into many individual smaller subnetworks or subnets.

Address classes give us a way to break the total global IP space into discrete networks.

Network ID – used to identify networks

Host ID – used to identify individual hosts.

Subnet ID

10.0.1.10 (10.0 is the network ID, 1.10 is the host ID)

In a world with subnetting, some bits that would normally comprise the host ID are actually used for the subnet ID.

Subnet Masks – 32-bit numbers that are normally written out as four octets in decimal

Each part of the IP Address is an octet, which means that it consists of eight bits.

The number 9 in binary is just 1001, but since each octet needs eight bits, we need to pad it with some zeros in front.

The size of a subnet is defined by the subnet mask.

A single 8-bit number can represent 256 different numbers, or more specifically, the number 0-255.

• Since that subnet mask represents 27 ones followed by five zeros, a quicker way of referencing this is with the notation /27. The entire IP and subnet mask could be written out as 9.100.100.100/27.

## Basic Binary Math

0 or 1, binary or base 2

### Decimal

8\;bit\;is\;2^8 = 256
4\;bit\;is\;2^4 = 16
16\;bit\;is\;2^16\ = 65536

decimal – base 10

binary – base 2

In binary:

The basic equation is x or y = z. If either x or y is true, then z is true, otherwise, it’s false.

In Binary, 1 or 0 = but 0 or 0 equals 0. 1 and 1 = 1, but 1 and 0 = 0, 0 and 0 = 0.

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