IP Addresses and Subnet Masks

Study Notes

An IP address is an identifier for a computer or device on a network, consisting of 32-bit numerical addresses written as four numbers separated by dots.
Each group of numbers separated by dots is called an octet, with a numerical range of 0-255.
An IP address is divided into two parts: the network address (or network ID) and the host address (or host ID).
The network address is a unique number assigned to a network, while the host address is assigned to hosts within that network, such as computers, servers, tablets, routers, etc.
A subnet mask is a number that looks like an IP address and reveals how many bits in the IP address are used for the network part by masking the network portion of the IP address.
In the world of computers and networks, IP addresses and subnet masks are meaningless in decimal format, as computers and networks only understand binary format (1s and 0s).
To convert IP addresses and subnet masks to binary format, each octet is represented by a number, with each bit in the octet having a value of 1 or 0.
By manipulating the 1s and 0s in the octet, a numerical range of 0-255 can be achieved.
To determine which part of the IP address is the network part, the binary digit of the subnet mask is checked; if it's a 1, it indicates the position in the IP address that defines the network.
By striking out the digits in the IP address that correspond to the 1s in the subnet mask, the network part of the IP address can be revealed.
The 1s in the subnet mask indicate the network address, while the 0s indicate the host addresses.
Subnet masks are used to break down a large network into smaller networks or subnets, allowing for better management and reducing network congestion.
Without subnet masks, a large network would have to be physically separated using routers, which would be inefficient and prone to errors.
Subnet masks allow routers to intelligently direct data to the correct subnet, reducing network traffic and improving communication between devices.- Subnet masks can be changed by borrowing bits from the host part to create subnets, allowing for more networks.
The default subnet mask gives 1 network with 256 hosts, but 2 hosts are reserved, leaving 254 usable hosts.
Borrowing 1 bit from the host part divides the network into 2 subnets with 126 hosts each.
Borrowing 2 bits from the host part divides the network into 4 subnets with 62 hosts each.
Borrowing 3 bits from the host part divides the network into 8 subnets with 30 hosts each.
Borrowing 4 bits from the host part divides the network into 16 subnets with 14 hosts each.
Borrowing 5 bits from the host part divides the network into 32 subnets with 6 hosts each.
Borrowing 6 bits from the host part divides the network into 64 subnets with 2 hosts each.
Borrowing 7 bits from the host part divides the network into 128 subnets, but with 0 usable hosts.
The more bits borrowed from the host part, the more networks that can be created, but the number of hosts per network is halved.
In the business example, borrowing 2 bits from the host part creates 4 subnets, but only 3 are needed, resulting in a subnet mask of 255.255.255.192.
IP addresses and subnet masks come in 5 classes: A, B, C, D, and E, with classes A, B, and C being used commercially.
Class A IP addresses can support up to 16 million hosts, with 3 octets used for hosts, making the host part very large.
Class B IP addresses can support up to 65,000 hosts, typically used by medium to large organizations.
Class C IP addresses can support up to 254 hosts, typically used by small organizations and homes with few hosts.
Subnet masks can also be expressed in CIDR (Classless Inter-Domain Routing) notation, also known as slash notation.
CIDR notation is a shorter way to write a subnet mask, using a forward slash and a number that represents the number of 1's in the subnet mask.

Description

Learn about IP addresses, subnet masks, and how they work together to identify devices on a network. Understand the concept of network and host addresses, and how subnet masks are used to divide networks into subnets.