WHAT HOW WHY Subnet mask ? | IP address | Default Gateway | Network Address

A subnet mask is a 32-bit value used in conjunction with an IP address to divide an IP network into subnets. It is a fundamental component of IP addressing and is used to determine which part of an IP address represents the network portion and which part represents the host portion.

Here are the key points to understand about subnet masks:

Binary Representation: A subnet mask is expressed as a 32-bit binary value, with consecutive bits set to 1 indicating the network portion and consecutive bits set to 0 representing the host portion. For example, a subnet mask of 255.255.255.0 is represented in binary as 11111111.11111111.11111111.00000000.

Network and Host Portions: By comparing the corresponding bits of the subnet mask and IP address, you can determine the network and host portions. The bits in the IP address that correspond to the 1s in the subnet mask represent the network portion, while the bits corresponding to the 0s represent the host portion.

Subnetting: Subnet masks are essential for subnetting, the process of dividing a network into smaller subnets. Subnetting allows for efficient utilization of IP addresses, improved network management, and enhanced security.

Classful and Classless Subnetting: In the early days of IP addressing, subnet masks were determined based on the IP address class (Class A, B, or C). This is known as classful subnetting. However, with the introduction of Classless Inter-Domain Routing (CIDR), subnet masks can have any length, providing more flexibility in network design. This is referred to as classless subnetting.

CIDR Notation: Subnet masks are often represented using CIDR notation, which consists of the IP address followed by a slash (/) and the number of network bits in the subnet mask. For example, a subnet mask of 255.255.255.0 is represented as /24 in CIDR notation, indicating that the first 24 bits are part of the network address.

Default Subnet Masks: Each IP address class has a default subnet mask associated with it. For example, Class A addresses have a default subnet mask of 255.0.0.0, Class B addresses have a default mask of 255.255.0.0, and Class C addresses have a default mask of 255.255.255.0. These default masks can be modified when subnetting.

By applying a subnet mask to an IP address, devices can determine which devices are on the same local network (in the same subnet) and which devices require routing to communicate across different subnets. Subnet masks are crucial for IP address allocation, network segmentation, and efficient utilization of IP resources in complex networks.