Explain the concept of subnetting, default mask and subnet mask.

Concept of Sub-netting

Sub-netting is the practice of dividing up a network into two or more networks. Common advantages of sub-netting include enhancing routing efficiency, network management control, and improving network security.

The main purpose of sub-netting is to help relieve network congestion. Congestion used to be a bigger problem than it is today because it was more common for networks to use hubs than switches. When nodes on a network are connected through a hub, the entire network acts as a single collision domain. Common advantages of sub-netting include enhancing routing efficiency, network management control, and improving network security.

Concept of Subnet Mask

Every device has an IP address with two pieces: the client or host address and the server or network address. IP addresses are either configured by a DHCP server or manually configured (static IP addresses). The subnet mask splits the IP address into the host and network addresses, thereby defining which part of the IP the address belongs to the device and which part belongs to the network.

The IP address, subnet mask and gateway or router comprise an underlying structure—the Internet Protocol—that most networks use to facilitate inter-device communication.

When organizations need additional sub-networking, sub-netting divides the host element of the IP address further into a subnet. The goal of subnet masks is simply to enable the sub-netting process. The phrase “mask” is applied because the subnet mask essentially uses its own 32-bit number to mask the IP address.

 

Concept of Default Mask

The default subnet masks are three subnet masks that correspond to the standard Class A, B, and C address assignments. These default masks are summarized in the table below.

Table- The Default Subnet Masks

Class	Binary	Dotted-Decimal	Network Prefix
A	11111111 00000000 00000000 00000000	255.0.0.0	/8
B	11111111 11111111 00000000 00000000	255.255.0.0	/16
C	11111111 11111111 11111111 00000000	255.255.255.0	/24

 

Most home networks use the default subnet mask of 255.255. 255.0. However, an office network may be configured with a different subnet mask such as 255.255. 255.192, which limits the number of IP addresses to 64.

A subnet mask is not actually required to use one of these defaults because the IP address class can be determined by examining the first three bits of the IP address. If the first bit is 0, the address is Class A, and the subnet mask 255.0.0 is applied. If the first two bits are 10, the address is Class B, and 255.255.0.0 is used. If the first three bits are 110, the Class C default mask 255.255.255.0 is used.