Networking

IPv4 stands for Internet Protocol version 4.  It consists of 4 groups of numbers, separated by a dot.  Each group occupies 1 byte in size, so the values can be between 0 and 255.

The lowest IPv4 address possible is 0.0.0.0, the highest IPv4 address possible is 255.255.255.255.  However, those addresses are not used.

Due to IPv4 address shortage (we can have a maximum of 4294967295 direct addresses) subnetting has been introduced.  Subne

Due to IPv4 address shortage, subnetting has been introduced.   We can have a maximum of 4294967295 direct addresses.  That might seem a lot and that's what was thought also when internet was introduced.  But since the explosion of the internet, a solution had to be found to avoid internet address waste.  Subnetting was born.

Subnetting is a mechanism to split up a network in smaller chunks to avoid wasting too many valuable addresses.  Suppose you have a network with only 10 PC's and you would occupy one byte (octet) to assign those addresses, it means you would waste 246 addresses that otherwise could be used in other networks.  That's where subnets come in.

Subnetting is also used to avoid network congestion.  Suppose you have a network with 256 devices connected and one device wants to talk to another device, the first device will send out a broadcast message asking who has a certain IP address.  That broadcast would arrive at all 256 devices and they all have to answer back that they're not the owner of the requested IP address, except 1 device.  This is a huge waste of bandwidth.

By applying subnetting you can reduce the amount of devices on a network and as such also reduce the amount of communication from 256 to the maximum needed devices, say 10.

Another advantage of subnetting is security.  Perhaps a company doesn't want devices in network A to communicate to devices in network B.  This could also be done by subnetting because a device cannot as such find another device which is not in the same network range.

IPv4 has 5 different classes of IP ranges: Class A, B, C, D and E

Classes D and E are not available for public internet as they're reserved for multicasting purposes (class D) and research purposes (class E).

The 5 classes are divided into the following IP address groups and their respective default subnet masks (for classes A, B and C):

Class A

IP range: 0.0.0.0 to 127.255.255.255

Default subnet mask: 255.0.0.0

Class B

128.0.0.0 to 191.255.255.255.255

Default subnet mask: 255.255.0.0

Class C

192.0.0.0 to 223.255.255.255

Default subnet mask: 255.255.255.0

Class D

224.0.0.0 to 239.255.255.255

Class E

240.0.0.0 to 255.255.255.255