An Overview of Subnet Classes

In order to effectively manage customer networks, it’s crucial that managed services providers (MSPs) have a firm grasp of internet protocols. You’ll need to understand how to subdivide a customer's network into subnets if you want to help your customers improve on essential operating functions. That being said, there’s no one-size-fits-all approach for using subnets to organize a network. In fact, it can be quite a complicated process with many technical quirks. Before you attempt to tackle it all, it’s important to understand IP networks and their unique classes. 

What is an IP subnet?

An IP subnet, often called a subnetwork, is a subdivision of an IP network. They can be best understood as the logical organization of connected network devices. Subnetting allows a company to break its large network into smaller, more organized divisions. The advantages of subnetting include: 

• Improved efficiency: By breaking large networks into smaller ones, your customers can simplify basic tasks like troubleshooting. 
• Better security: Subnetting can help customers more easily deploy security measures such as firewalls.
• Reduce network traffic: Smaller networks equate to smaller broadcast domains. This can free up network congestion. 

The implementation of good subnetworking can go a long way in the day-to-day operations of your current and potential customers. 

First, it's important to understand some of the nuances about IP addresses in order to fully grasp how subnets can be implemented. Because IP is a connectionless protocol designed to operate without a central directory or monitor, networks rely on numerical addresses to deliver data across connected devices. These addresses allow a system to be recognized by other systems on the IP or on a specific network. It’s helpful to think of these numbers like a mailing address that identifies where postal mail comes from and where it should be delivered. The two primary versions of IP addresses are IPv4 and IPv6.  

IP addresses have two components: a network prefix and a host identifier. The prefix often takes up the majority of bits in the address. IPv4 addresses are designated by a 32-bit specification which is represented by 4 octets, or 8-bit units of digital information, ranging from 0-255. These addresses are frequently shown in decimal form rather than in binary, but for subnetting, it’s helpful to make the conversion. 

Subnets are implemented by borrowing bits from the host end of an IP address in order to divide the larger network into smaller subnetworks. This is accomplished with the use of a subnet mask. The new, modified IP address will have the same network and host components as before, but will now feature a subnet component as well.  

What are the classes of networks?

There are five classes of subnetworks: Class A, Class B, Class C, Class D, and Class E.  Each class relates to a specific range of IP addresses. Classes A, B, and C are used the most often by different networks.

Subnet classes are made unique by the number of bits their IP addresses have dedicated to a network and the number of bits dedicated to hosts.  They each have a default subnet mask. Classes can be identified by the number in the first octet of their address.

• Class A: First Octet Value 0-126
• Class B: First Octet Value 128-191
• Class C: First Octet Value 192-233
• Class D: First Octet Value 224-239
• Class E: First Octet Value 240-255

Note that 127 is not accounted for because it denotes a loopback address.