Subnet Mask

An IP (Internet Protocol) address is a unique identifier for a single device (node or host connection) on an IP network. It is a 32 bit binary number that ranges from 0 to 4294967295. This means that theoretically, the Internet can contain approximately 4.3 billion unique objects This binary number is usually represented as 4 decimal values, each representing 8 bits (octets), in the range 0 to 255 separated by decimal points. This is known as “dotted decimal” notation. IP address is a communications protocol used from the smallest private network to the massive global Internet.

Increments of an IP Address:

0.0.0.0

0.0.0.1

…increment 252 hosts…

0.0.0.254

0.0.0.255

0.0.1.0

0.0.1.1

…increment 252 hosts…

0.0.1.254

0.0.1.255

0.0.2.0

0.0.2.1

…increment 4+ billion hosts…

255.255.255.255

Subnetting and Subnet Mask

A subnetwork, or subnet, describes networked computers and devices that have a common, designated IP address routing prefix. Every IP address consists of two parts, one identifying the network and one identifying the node. The Class of the address and the subnet mask determine which part belongs to the network address and which part belongs to the node address. Routers are used to manage traffic and form borders between subnets.

Subnetting is used to break the network into smaller, more efficient subnets to prevent excessive rates of Ethernet packet collision in a large network. These subnets can be arranged hierarchically, with the organization’s network address space partitioned into a tree-like structure.

A significant feature of subnetting is the subnet mask. Similar to IP addresses, a subnet mask contains four bytes (32 bits) and is often written using the same “dotted-decimal” notation. Applying a subnet mask to an IP address allows you to identify the network and node parts of the address. The network bits are represented by the ones in the mask, and the node bits are represented by the zeros which are identical to the subnet length.

A subnet mask cannot replace an IP address; however they do work together and not independently. Applying the subnet mask to an IP address splits the address into two parts, an “extended network address” and a host address. The subnet mask determines the size of a subnet and pinpoints where the end points on the subnet ar, if the IP address within the subnet is known. The mask aspect in a subnet mask comes from the fact that it conceals the host bits and leaves the Network ID that starts the subnet. If the beginning and size of the subnet is known, the end of the subnet (Broadcast ID) can be defined. The Network ID is the official designation for a particular subnet, and the ending number is the broadcast address that every device on a subnet listens to.

Uses of Subnet Masks

Identifies a Network
Isolates the Network ID and Host ID
Determines the number of host/terminals that could be used on the same network
Reduces Network traffic