This short article will attempt to explain the ideas behind subnets and make the subject a little less confusing. In order to forward packets, you need a route to each and every machine that you service. Now, it doesn't make sense to have routes to every individual machine. Instead, the local machines are grouped together as a range of IP addresses, and the gateway forwards packets to all machines in this range of addresses.
Gateways have to route packets as quickly as possible.
One of the ways to speed the process is to express each route in the routing table as a subnet , instead of a range of addresses. The Idea of a Subnet Let's take a range of IP addresses that we want to build a route for. We can see that, for all addresses in the range, most of the bits are common. This says that the range of addresses all have the first 21 bits in common, and that these 21 bits are 44.136.8. This also says that the first address in the range is 44.136.8.0.