Subnetting allows you to create multiple logical networks that exist within a single Class A, B, or C network.

Class A addresses are for networks with a large number of hosts. The first octet is the netid and the 3 remaining octets are the hostid.

Class B addresses are used in medium to large networks with the first 2 octets making up the netid and the remaining 2 are the hostid.

Class C is for smaller networks with the first 3 octets making up the netid and the last octet comprising the hostid.

Classful addressing works by dividing the IP address space into chunks of different sizes called classes.

Classless addressing is referred to as Classless Inter-Domain Routing (CIDR) and is done by allocating address space to Internet service providers and end users on any address bit boundary, instead of on 8-bit segments.

So 172.16.50.0 does not have to use the standard subnet mask of 255.255.0.0 which makes a Class B address space and which also puts it on the same network as 172.16.51.0 using the subnet mask of 255.255.0.0. Instead, by using classless addressing 172.16.50.0/24 puts these systems on a different network than 172.16.51.0/24 because the network names here are 172.16.50 and 172.16.51 which are different.

NAT stands for Network Address Translation and is a commonly used IP translation and mapping technology.

Using a device (such as a router) or piece of software that implements NAT allows an entire home or office network to share a single internet connection over a single IP address.

Port Address Translation is a feature of a network device that translates TCP or UDP communications made between hosts on a private network and hosts on a public network.

It allows a single public IP address to be used by many hosts on a private network.