In the world of networking, the concept of subnets plays a crucial role in efficiently managing and organizing IP addresses within a network. Subnetting allows network administrators to segment a large network into smaller, more manageable sub-networks, enhancing security, performance, and overall network administration. In this article, we will delve into the fundamental concept of subnets, explore their importance, and guide you through the process of calculating subnets.
What is a Subnet?
A subnet, short for sub-network, is a division of an IP network into smaller, isolated networks. Each subnet functions as an independent network within the larger network, complete with its range of IP addresses. Subnetting serves several essential purposes, including:
- IP Address Management: Subnetting allows efficient allocation and management of IP addresses. It prevents IP address wastage by allocating only the required number of addresses to each subnet.
- Security and Isolation: Subnets enhance security by isolating groups of devices. This isolation helps contain potential security breaches within a specific subnet, limiting their impact on the entire network.
- Broadcast Domain Control: Subnets limit the broadcast domain size. Smaller broadcast domains result in reduced network traffic and more efficient use of bandwidth.
- Performance Optimization: By segmenting a large network into smaller subnets, network traffic is localized, leading to improved network performance and reduced latency.
The Need for Subnets
What exactly is subnetting? Subnetting is taking an IP network and subdividing it into smaller IP networks called subnetworks, or subnets. Every IP network, or subnet, is a broadcast domain. A broadcast domain is a collection of devices that can receive broadcast traffic from each other. Broadcast traffic is traffic that is delivered to every device on the network.
Having a single broadcast domain, or a “flat network,” presents two main problems.
- 1. In a single large broadcast domain, there is a large amount of broadcast traffic. Broadcast traffic is very inefficient and consumes large amounts of resources, such as bandwidth, processor cycles, and memory. In fact, enough broadcast traffic on a network can cause other applications, such as email, word processors, and spreadsheets, to be negatively impacted.
- 2. When all devices are part of the same broadcast domain, there are no protocol boundaries between devices, so implementing security policies is difficult. In other words, there is no easy way to protect one device from another device without using host-based mechanisms, such as host-based firewalls, permissions, rights, and anti-virus. These methods serve a valuable purpose, but they are not very efficient, and they can degrade the performance of the host.
The solution to these problems is to break the single large broadcast domain into several smaller broadcast domains. By doing this, the number of devices connected to each broadcast domain is smaller. This reduces the amount of broadcast traffic, improving the performance of all devices on the network. Additionally, a boundary between devices is created, which greatly improves and simplifies the implementation of security policies.
As an analogy, imagine a single room, and in this room are five different groups of people; one group in each corner and one group in the center. Each group of people has a microphone and is discussing a different topic. If you were a member of one of the groups, picture how difficult it would be to hear people in your group, concentrate on your topic, and share confidential information.
Now imagine the single room being separated into five smaller rooms. Each group now has its own room with a door and can communicate without competing with the other groups. Each person can hear and concentrate better and more easily keep confidential information within the group.
The concept of dividing a large room into smaller rooms is the same as the concept of dividing a large broadcast
domain (IP network) into smaller broadcast domains (subnets).
How to Calculate Subnets
Subnetting involves dividing an IP address range into smaller, manageable segments. The process requires two primary components: the original IP address and a subnet mask. The subnet mask is a 32-bit binary number that designates the network and host portions of an IP address.
Here’s a step-by-step guide to calculating subnets:
- Choose a Subnet Mask: The subnet mask consists of network bits (represented by ‘1’ in binary) and host bits (represented by ‘0’ in binary). The number of network bits determines the size of the subnet. Common subnet mask formats include CIDR (Classless Inter-Domain Routing) notation (e.g., /24) or the traditional dotted-decimal format (e.g., 255.255.255.0).
- Determine the Network Portion: Use the chosen subnet mask to determine the network portion of the IP address. Perform a bitwise AND operation between the subnet mask and the IP address to obtain the network address.
- Identify Host Range: Calculate the number of available host addresses within the subnet. Subtract 2 from the total (one for the network address and one for the broadcast address) to get the usable host range.
- Broadcast Address: The broadcast address is the highest address in the subnet. It is obtained by setting all host bits to ‘1’ in the binary representation of the network portion.
- Subnetting Practice: Let’s say you have the IP address 192.168.1.0/24. This means you have 24 network bits and 8 host bits. The subnet mask in binary is 11111111.11111111.11111111.00000000. Performing a bitwise AND operation with the IP address gives you the network address: 192.168.1.0. The usable host range is 192.168.1.1 to 192.168.1.254, and the broadcast address is 192.168.1.255.
Example 1
192.168.1.0/24
Subnet mask: 255.255.255.0
Hosts: 2^(32-24) = 2^8 = 256
Active hosts: Hosts – 2 = 254
Network ID (first address): 192.168.1.0
Broadcast ID(last address): 192.168.1.255 (0 to 255 is 256 integers.)
Example 2
192.168.1.16/28
Subnet mask = 255.255.255.240
Hosts: 2^(32-28) = 2^4 = 16
Active hosts = Hosts – 2 = 14
Network ID: 192.168.1.16
Broadcast ID: 192.168.1.31 (16 to 31 is 16 integers)
Optimizing Subnet Design
When designing subnets, consider the following tips for efficient network management:
- Plan for Growth: Allocate enough addresses to each subnet to accommodate future growth. Avoid creating subnets that are too small and could quickly run out of available addresses.
- Hierarchy and Organization: Create a logical hierarchy for subnets. Group devices based on their functions, departments, or locations to enhance network organization.
- Minimize Broadcast Domains: Keep the number of devices within a subnet manageable to prevent excessive broadcast traffic. Subnetting helps contain broadcast domains and improves network performance.
What Are the Advantages of Subnetting?
Why is subnetting important? Subnetting has many advantages, but these three are the most significant:
Performance
Subnets make networks more efficient. Subnetting allows traffic to travel a shorter distance, not having to pass through unnecessary routers along the way. This improves the performance by reducing network congestion and speeding up traffic.
Organization
Subnetting makes it easier and more efficient to group different devices. For example, a company might have an accounting department with some privileges that other departments should not have. A subnet containing just the accounting department would ensure that other devices cannot access that network. This makes the organization more efficient and allows the network to implement exclusivity.
Security
Because subnets separate and group smaller networks, it is easier to isolate and identify threats in a particular network.
What Are the Disadvantages of Subnetting?
Subnetting is quite expensive and requires professional knowledge to implement.
Subnetworks can be wasteful, depending on how you divide them up. For example, each subnetwork requires a network ID and a broadcast ID, two IPs that it needs to reserve from the total pool.
Conclusion
Subnetting is a fundamental concept in networking that empowers administrators to effectively manage and optimize IP address allocation within a network. By dividing a large network into smaller subnets, organizations can enhance security, performance, and overall network administration. Understanding the process of calculating subnets allows network professionals to design and maintain efficient and scalable networks that meet the demands of modern technology.