What is a Network Class?

Quick Definition: Network classes are predefined categories of computer networks that are defined by specific ranges of IP addresses. These classes, namely Class A, B, and C, help organize and allocate IP addresses in a hierarchical manner. This provides efficient routing and management of network resources.

Network classes have played a fundamental role in networking since their inception in 1981. In short, a network class is any grouping of IP addresses that fill a particular role. This is done through a concept known as subnet masking, which we'll cover in depth.  

Initially, network classes were divided into classes A, B, and C. A network was assigned a certain class depending on the size and complexity of the class itself. As with everything in networking, though, there’s more to it than that. 

Read on to understand network classes and their counterpart CIDR classes. The following information is crucial for anyone about to take the CCNA exam, Network+ Exam, or work within a mile of the server room. So, let’s start with a more foundational understanding of classes by discussing IP addressing. 

The Role of IP Addressing in Network Classes

Network classes and the TCP/IP protocol have been intertwined since the advent of networking. An IPv4 address looks like this:

While this likely looks familiar to you, let’s break it down and discuss how it relates to network classes.

An IPv4 network address comprises four binary octets (32 bits). For the sake of simplicity, they are written in a decimal number system so we humans can easily read them. However, a computer reads this in binary, like this:

As an aside, the computer is not literally seeing 1’s and 0’s. Instead, the 1’s and 0’s are voltage differentials representing whether a bit is “on” or “off.”

IPv4 addresses are still widely used, however, they are slowly being replaced by IPv6 addresses, which look like this:

For the sake of readability, the empty bits are omitted and shortened to this: 

IPv6 carries 128 bits instead of 32 like IPv4, so it can accommodate a far wider range of devices in a world where there are far more devices with NIC cards than ever before.

As you can see with both IPv4 and IPv6, nearly an infinite amount of IP addresses can be chosen on a network. This can get messy fast, and it can get confusing to remember which nodes on a network have a relationship with one another. 

Network classes were created as a way to categorize IP addresses by how large the network is. Network classes were the law of the land until they were superseded by CIDR classes. Let’s discuss some of their benefits.

What Exactly are Network Classes?

Network classes refer to an early classification system of networks that divided networks by size into Class A, Class B, and Class C. The amount of IP combinations goes from largest to smallest, so Class A has the most combinations. For network classes, IP addresses are divided into a Network ID and a Host ID. 

For example, the IP address 192.1.12.70, we can say 192.1.1 is the Network ID, and 70 is the Host ID. The key to network classes is knowing when the Network ID ends and the Host ID starts. The following table shows an IP address example for each class, with the Network ID bolded.

Let’s break this table down a bit. As you can see, Class A has the most IP addresses. That’s because only the first octet is reserved for the network ID–the rest of the octets can be reserved as potential nodes on the network. The larger the network, the more nodes will be utilized. For example, Microsoft will have far more computers on its network than some mom-and-pop stores.

The last column illustrates the bit reservations per class. In the Class C example, every octet is reserved except for the last one. So let’s say you had five computers on that Class C network, the IP address would look like this.

The network would still have space for another 251 nodes, but observe how each of the first three octets are the same; that’s a dead giveaway for a Class C network. The subnet mask denotes that the first three octets are reserved. 

Lastly, Class D and Class E. Class D IP addresses are reserved for multicast operations.

Class E is only for experimentation on new protocols, and nodes should not be assigned these nodes in a production environment.

The Evolving Role of Network Classes in Modern Networking

The concept of network classes was an excellent solution when we had many IP addresses to deal with. However, now we have an absolutely huge amount of IP addresses to deal with. That’s why CIDR notation (Classless Interdomain Routing) was created back in 1993, and classful networks have been slowly phased out since.

CIDR notation removed the strict boundaries set in place by classful networking and allowed for more efficient use of IP addresses. Along with CIDR notation, subnetting has brought numerous advantages to the role of network classes. Subnetting is the practice of taking large networks and dividing them into smaller networks using Variable Length Subnet Masking (VLSM).

Lastly, IPv4 is slowly being supplanted by IPv6. IPv6 offers a wider range of possible addresses. This is a particular boon in the age of IoT, when pretty much everything from guitars to shoes have WiFi in them. IPv6, subnetting, and CIDR notations have taken the core principles of classful routing and expanded them to accommodate a limitless amount of internet devices.

How Does Subnetting Work with Network Classes

Let’s take a look at the term Variable Length Subnet Masking (VLSM). “Variable” is bolded because it is distinct from the classful network with “static” or concrete subnet masking. For example, Class A Networks has a subnet mask 255.0.0.0, meaning the first octet is reserved as the network ID.

That idea has been adopted by CIDR, except CIDR provides more flexibility by allowing the network administrator to determine the size of the subnet. This is generally written like this:

That means the subnet mask is 255.255.255.0; the first three octets are reserved. So this shorthand CIDR notation means the following in plain English: “My network can reserve IP addresses in the range of 192.169.1.0 to 192.169.1.255”. The smaller the CIDR number, the more IP addresses the network can accommodate. For more information on CIDR Notation, check out this post. 

Network Classes in Certification and Advanced Networking

I cannot emphasize enough how important network classes are to the CCNA, Network+, and just about any other networking certification. Understanding how and when to divide networks is critical to the environment’s stability, scalability, and security.

Understanding network classes will provide a historical foundation as to why things are done the way they are today. Additionally, virtually every IP address now is written in CIDR notation, and reading it needs to become second nature. 

Another thing to consider is you won't always be working on new technology (Unless you’re a very lucky person!) Often, antiquated documents will need to be read and understood to get a grasp of the current network. These documents will contain network concepts such as static IP masking and classful networks, which will need to be understood for troubleshooting.

Final Thoughts

Network classes are a wide and varied topic, but a necessary one for passing the Network+ Exam and understanding networks in general.

Here are the key takeaways. Class A, B, and C are historical concepts used to divide up and organize networks by a static subnet mask. Class A has by far the most IP addresses available, while Class C has the least. That’s because Class A has a subnet mask of 255.0.0.0, while Class C has a subnet mask of 255.255.255.0. 

CIDR notation and subnetting were invented in 1993 to deal with IP address allocation and efficiency because the rigidity of Classful Networks had become too much to bear. CIDR notation provides a far more flexible method of dividing subnets by allowing the subnet mask to be variable, instead of concrete.

Every network topology requires organization for documentation, troubleshooting, maintenance purposes, and more. Understanding network classes and CIDR will level up your knowledge, assist in passing exams, and make you an invaluable asset to any IT organization.

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