IP addresses are in simple terms, how computers know how to talk to each other.
For example, if you have on your home network a computer with the IP 192.168.0.1 and another with 192.168.0.2, these computers can go via the gateway to send messages between each other.
There are two kind of IP address spaces you need to care about, public and private.
The key difference between the two, is that private IP addresses can be duplicated across the internet, because they're only ever exposed internally, in addition to being "reserved".
The most common type of IP address out there, is IPV4
A IPV4 address is structured with 4 octets. Each of these octets can contain the values 0-255, meaning that there are only 256*256*256*256 = 4,294,967,296 available IPV4 addresses.
An IPV4 address is made of 4 octets. Each octet is one block of 8 bits, and together they build the full address.
| RFC 1918 name | IP address range | Number of addresses |
|---|---|---|
| 24-bit block | 10.0.0.0 - 10.255.255.255 | 16,777,216 |
| 20-bit block | 172.16.0.0 - 172.31.255.255 | 1,048,576 |
| 16-bit block | 192.168.0.0 - 192.168.255.255 | 65,536 |