Introduction: About Subnetting

Let’s take a look at “What is Subnetting?” and see if you can benefit from it! Various networking professionals use subnetting in various ways. Several organizations are training their IT Aspirants with these skills to enhance their network security.

In the end, we will introduce you to a reputed training institute offering a dedicated training program related to networking skills. What are we waiting for? Let’s explore more!

What is Subnetting in Networking?

The process of logically splitting a single, big IP network into smaller, more effective subnetworks, or "subnets," is known as subnetting. This is accomplished by employing a subnet mask to extend the network section of an IP address by borrowing bits from the host portion.

What is Subnetting in Networking

The main objectives are to increase security by isolating network segments, improve network performance by lowering broadcast traffic, and enable more effective IP address management. Let’s take a closer look at “What is Subnetting?”

What is a Subnet Mask?

Similar to an IP address, a subnet mask is a 32-bit value that separates the host and network parts of an IP address. A device can rapidly ascertain which portion of the address designates the particular network segment by executing a logical AND operation between the IP address and the subnet mask.

What is Subnetting in Computer

It is essential to the subnetting process because it enables devices to ascertain whether a destination host is on the local network or whether traffic needs to go via a router.

The Mechanics of Subnetting

S.No.	Mechanics	What?
1.	The Core Concept: Borrowing Host Bits	In order to borrow bits from the host section of the IP address and utilize them for the network portion, subnetting moves the border specified by the subnet mask.
2.	Calculating New Subnets and Hosts	The number of usable hosts per subnet is computed as 2^h - 2, where h is the leftover host bits, and the number of available subnets is calculated as 2^n, where n is the number of borrowed bits.
3.	Identifying Subnet Components	Each subnet range starts with a Network Address (all host bits 0) and concludes with a Broadcast Address (all host bits 1). Devices can use the remaining addresses.

How Does Subnetting Work?

In the following ways, subnetting works:

Borrowing Host Bits: The first step in the procedure is to "borrow" bits from the original IP address's host section and add them to the network portion (which is determined by the subnet mask).
Creating the Subnets: You can use a single network address space across several physical or virtual segments by creating a new, smaller logical subnet with each distinct combination of the borrowed bits.
The Subnet Mask Change: In order to inform routers and devices of the precise location of the new network boundary, the subnet mask is modified to incorporate these newly borrowed bits (e.g., changing from a /24 to a /26).
Calculating Addresses: The formula 2n (where n is the borrowed bits) is used to determine the number of new subnets, and 2^h - 2 (where h is the remaining host bits) is used to determine the number of usable hosts per subnet.
Network Identification: When a device sends a packet, it quickly determines the Network Address (or Subnet ID), which instructs it whether to send the data locally or forward it to a router, by performing a bitwise AND operation on the destination IP address and its subnet mask.

Advanced Subnetting Concepts

S.No.	Factors	What?
1.	Variable Length Subnet Masking (VLSM)	Enables the division of a network into subnets of various sizes, maximizing the use of IP addresses by assigning just the host addresses required for each segment.
2.	Classless Inter-Domain Routing (CIDR)	Used a network prefix length (such as /24) to designate the network and host sections in place of the previous class-based method, streamlining routing and increasing IP address efficiency.
3.	Supernetting (Route Aggregation)	Reduces the number of entries in routing tables by combining several smaller, adjacent IP networks into a single, larger network block (a process known as route summarization).
4.	Subnet Zero and All-Ones Subnet (The First and Last Subnets)	The first subnet (all borrowed subnet bits are 0) and the last subnet (all borrowed subnet bits are 1), which were previously reserved, are now often usable in accordance with CIDR best practices.
5.	/31 Subnets (Point-to-Point Links)	A /31 subnet, which is defined in RFC 3021 and contains just two IP addresses, is ideal for point-to-point links between two routers since it does away with the need for network and broadcast addresses.
6.	IPv6 Subnetting	Focuses on the 64-bit length of the Interface ID (the host portion), while subnetting mostly entails modifying the 16-bit Subnet ID field inside the 64-bit Network Prefix.

Subnetting in Practice

In the following ways, you can practice subnetting:

● Determine Requirements: Make sure you account for future development by counting the hosts required for each physical segment (LAN, WAN link) and the overall number of required subnets.

● Design the VLSM Scheme (Variable Length Subnet Masking): To avoid IP address waste and guarantee effective address use, allocate the largest subnets first, giving each segment the most appropriate prefix (such as /24, /27, or /30).

● Implementation & Configuration: All network devices (hosts, switches, and routers) should have the computed network addresses, subnet masks, and default gateways applied to them.

● Documentation and Review: Using tools like ping and traceroute, confirm connectivity across all subnets and record the entire IP addressing scheme (Network ID, mask, broadcast, usable range, and allocated static addresses).

Advantages of Subnetting

S.No.	Advantages	How?
1.	Reduced Network Congestion	By restricting broadcast traffic to smaller pieces, subnetting enhances network performance by avoiding superfluous data from overwhelming the entire system.
2.	Improved Network Security	Limiting access and containing security breaches to a particular subnet enables administrators to isolate portions of the network.
3.	Efficient IP Address Utilization (VLSM)	You can minimize waste by assigning exactly the correct number of addresses to each segment by utilizing Variable Length Subnet Masks (VLSM).
4.	Enhanced Network Management	It is easier and more targeted to debug, maintain, and apply policies when a big network is divided into smaller, logical units.
5.	Optimized Routing	Routers can make quicker, more accurate forwarding decisions because of smaller, unique subnets, particularly when supernetting is used to aggregate them (CIDR).
6.	Scalability and Flexibility	Without re-addressing the entire network, subnetting enables methodical expansion and the simple inclusion of additional departments or locations.

What is Subnet Calculator?

The Network ID, Broadcast Address, and range of acceptable host IP addresses are just a few of the important IP network parameters that may be quickly ascertained with the help of a digital instrument or piece of software called a Subnet Calculator.

It assists network administrators in designing and implementing IP addressing schemes by calculating the resulting subnet boundaries by entering an IP address and a subnet mask (or prefix length).

For activities involving Classless Inter-Domain Routing (CIDR) and Variable Length Subnet Masking (VLSM), it is crucial.

How To Calculate Subnet Mask?

S.No.	Factors	How?
1.	Identify the CIDR Prefix Length	Find the / number (the prefix length, such as /24), which represents the total number of successive network bits that need to be set to 1.
2.	Determine the Octet Boundaries	Write out 32 bits in binary (four 8-bit octets), using 0s to fill in the leftover bits and 1s to match the prefix length.
3.	Convert Each Octet to Decimal	Transform each 8-bit octet back into its conventional decimal number from its binary value, which is a collection of 1s and 0s (for example, 11111111 becomes 255).
4.	Assemble the Subnet Mask	To create the final subnet mask (such as 255.255.255.0), combine the four decimal octet numbers, separated by dots.

Future of Subnetting

Subnetting's future is still very important, mainly shifting its emphasis from address conservation (since IPv4 is running out) to network organization and security. Subnetting is still an essential technique for effective route aggregation, logical network segmentation, and enhancing network administration and performance despite IPv6's gradual but steady deployment.

Address planning is made much simpler by the typical IPv6 subnet size of /64, which shifts the focus of subnetting calculations from the number of hosts per segment to the number of required subnets.

Conclusion

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Frequently Asked Questions

About What is Subnetting?

How does subnetting improve network security?

In the following ways, subnetting improves network security:

a) Enables Network Segmentation & Isolation,

b) Restricts Lateral Movement of Threats,

c) Facilitates Granular Access Control (ACLs),

d) Reduces the Scope of Compliance Audits, and

e) Simplifies Threat Detection & Incident Response.

What is the difference between VLSM and FLSM?

While VLSM permits varying subnet masks on separate subnets, leading to a varied number of hosts and improved IP address utilization, FLSM employs the same subnet mask for all subnets, resulting in a fixed, equal number of hosts per subnet.

Can subnetting help with IP address conservation?

Yes, a subnetting approach called Variable Length Subnet Masking (VLSM) is intended to preserve IP addresses by assigning only the required number of hosts per segment, hence avoiding the wastage of large blocks of addresses.

How does subnetting affect network performance?

In the following ways, subnetting affects network performance:

a) Reduces Broadcast Traffic & Congestion,

b) Improves Routing Efficiency,

c) Enhances Bandwidth Utilization,

d) Enables Traffic Prioritization, and

e) Simplifies Troubleshooting & Management.

What are the challenges of subnetting in large networks?

The following are some of the challenges of subnetting in large networks:

a) Complexity of VLSM Design & Planning,

b) Increased Routing Table Size,

c) Difficult & Error-Prone Documentation,

d) Scalability & Flexibility Constraints, and

e) Higher Administrative Overhead.

How is subnetting implemented in IPv6?

In the following ways, subnetting is implemented in IPv6:

a) Fixed Interface ID (/64 Prefix),

b) Subnetting the Subnet ID Field,

c) Hierarchical Address Planning,

d) CIDR Notation is Standard, and

a) SLAAC Requirement.

What is Subnetting? How Does It Work? [2026 Updated]

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