Subnets and IP standards

A subnet allows the flow of traffic on a network to be divided into segments based on the physical topology of the network. This can improve the security and the performance of a network. Each subnet is assigned a mask. 

A subnet mask is used in conjunction with an IP address. 

For example - A subnet mask of 255.255.255.0 uses 24 bits for the network ID. This would leave 254 unique addresses (as 0 and 255 are reserved as generic and broadcast addresses) for devices or host computers on the network. 

A subnet mask is 'ANDed' with an IP address to separate the network ID from the full IP address. 

A subnet mask is applied independently to the IP address of the source and destination computers. 

An IP address is a unique numerical address which is used to identify a host computer or a network node that is trying to communicate over the IP on the Internet

There are currently two standards of IP address IPv4 and IPv6. 

IPv4 was first deployed in 1983 which provides more than 4 billion combinations for IP address. IPv6 was introduced for fears we would run out of addresses in 1999. IPv6 offers 340 trillion, trillion, trillion (340,000,000,000,000,000,000,000,000,000,000,000,000) unique addresses and expresses the 128 bits in hexadecimal string rather than binary. 

It is thought that by 2020, IPv6 will be the standard but as IPv4 and IPv6 are incompatible any device that uses IPv4 and the software applications for IPv4 which operate on the internet will have to be upgraded or replaced. 

IPv4 addresses are 32-bit numbers which are written in dotted-decimal notation. Each part represents an 8-bit binary pattern which gives the range 0-255 for each decimal number. 

Some IP addresses are reserved so, therefore, cannot be used for an individual network or host. 

127.x.x.x are used for private non-routable addresses only used for diagnostics with local networks

x.x.x.0 is the network identifier

x.x.x.255 is the broadcast address on that subnet where data is sent simultaneously to all subnetwork hosts

x.x.x.1 is conventionally the default router address