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.


What is a Class A IP address? 

A Class A IP address reserves 8 bits for a network with 24 bits dedicated to hosts. Its IP address spans from 0 to 126. The Class A subnet mask is Accordingly, Class A IP addresses are best used to serve incredibly large networks.

In comparison to Class A, Class B IP addresses are better suited to serving smaller networks since they reserve 14 bits for a network, which leaves only 18 bits for hosts. Network addresses for these range from 128 to 191. Consequently, the default subnet mask for Class B is In addition, Class C IP addresses are normally assigned to a very small-sized network. Their IP addresses range from 192 to 233 and their default subnet mask is

It’s important to keep in mind that although it seems counterintuitive, the less bits an IP address reserves for a network, the more apt it is to serve subnets on bigger networks. This is because subnets are implemented on the host side of an IP address (so more network bits means less bits for the host to offer a subnet mask).

What is the use of Class D and Class E IP addresses?

The uses of Class D and Class E IP addresses are mostly reserved for experimental purposes. For instance, a Class D IP address is almost exclusively reserved for multicasting applications. (Multicasting is a method of routing data on a computer network that allows a single or group of senders to communicate with a group of receivers). Unlike Classes A, B, and C, Class D is not available for use in normal networking operations. They don’t have subnet potential because there are no host bits within the Class D address space.

Class E is often cited as having been created for future use, research, and development. Although these IP addresses are reserved, their actual use has never developed. As a result, most network implementations disregard this class altogether. In fact, Class E is sometimes classified as illegal or undefined. The one exception is IP address, which can be used as a broadcast address (a network address in which devices connect to a multiple-access communications network).

Getting started with networking

If you are an MSP, you should be sure to do your research on the nuances of IP so you can help your customers take advantage of what subnetting offers. Developing a strong understanding of what goes into these network improvements is the first step in serving customers when they come asking for help with their networks.

Once your subnets are established, SolarWinds® RMM can help you with a number of networking tasks, for example using NetPath can help you ensure that all your subnets are running as expected and to spot any issues and quickly remediate them.

Explore our resource center for more information on network performance. Also read more about our IP Blacklist Prevention Solution.