TCP/IP stands for Transmission Control Protocol / Internet Protocol. It is a networking protocol that allows two computers to communicate. Let’s begin with IP addresses.

IP Address

An IP address is a string of 32 ones and zeros. Since 8 bits make a byte, we break down the string of 32 bits into 8 bit chunks for counting. If we were to count in base 10, the 8 positions would look like the table below, where each position has the value of a multiple of 10.

10000000	1000000	100000	10000	1000	100	10	1
1	1	1	1	1	1	1	1

But since we are counting in binary which is to say base 2, to convert 11101010 to a number, each position has the value of a multiple of 2.

128	64	32	16	8	4	2	1
1	1	1	0	1	0	1	0

128 + 64 + 32 + 8 + 2 = 234

To convert 131 to a binary number,

131 - 128 = 3

3 - 2 = 1

1 - 1 = 0

128	64	32	16	8	4	2	1
1	0	0	0	0	0	1	1

The IP address of a computer or device identifies the device on a particular network.

Network ID is the part of the network numbering system that has to be identical for every computer on that particular network.

Take for example the IP 232.25.208.15, this IP belongs to a particular device.

232.25.208.0 is the network ID, the idea is that no computer can have just a 0 as part of its numbering system as it is reserved for the network ID.

Host ID is the part of the IP address that changes for every individual device on the network.

A subnet mask is a string of 1’s followed by a certain number of 0’s.

255.255.255.000 – this is a /24 (pronounced as ‘wack 24’) subnet mask, we can have 254 hosts here (2^8 -2)

We can’t use 255 and 0 in our addressing because the IP address 0.0.0.0 is used as a wildcard to bind to all addresses while the IP address 255.255.255.255 is used to indicate a local broadcast.To understand more about the reason you can read about classful network design and CIDR.

255.255.000.000 – this is a /16 (pronounced as ‘wack 16’) subnet mask, we can have 65534 hosts here (2^16 -2)

The subnet mask get smaller for larger networks and it gets bigger for smaller networks.

The subnet mask allows the local machine to know if the destination is on the local network or a remote network.

Your router is what transmit data from one network to another hence it is also known as the default gateway.

Each host knows the default gateway so that it can forward traffic to remote networks.