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IP Address Classes A Through E, Explained

Why does an address starting with 192.168 look so familiar? The classful addressing system behind it, explained.

What classful addressing is

An early system for assigning IPv4 addresses that split the address space into five classes (A through E) based on the leading bit pattern. It has since been replaced by CIDR, but the class terminology is still commonly used when discussing private IP ranges or teaching networking basics.

Class A: starts with 0–127, for very large networks

The first octet ranges from 0 to 127 (1–126 in practice, since 0 and 127 are reserved), with a default subnet mask of 255.0.0.0 (/8). Each network can hold over 16.7 million hosts, and this class was historically assigned to major telecoms and government bodies.

Class B: starts with 128–191, for mid-sized networks

The first octet ranges from 128 to 191, with a default subnet mask of 255.255.0.0 (/16), allowing up to 65,534 hosts per network — historically assigned to universities and mid-sized organizations.

Class C: starts with 192–223, for small networks

The first octet ranges from 192 to 223, with a default subnet mask of 255.255.255.0 (/24), allowing up to 254 hosts per network — the most commonly cited class for small offices and home networks. The familiar private range 192.168.0.0–192.168.255.255 falls within Class C.

Class D: starts with 224–239, reserved for multicast

The range 224.0.0.0–239.255.255.255 is reserved exclusively for multicast group addresses, used when one sender transmits to many receivers at once. It is never assigned to an individual device like a computer or phone.

Class E: starts with 240–255, reserved/experimental

The range 240.0.0.0–255.255.255.255 was reserved from the start for future and experimental use and is not used for ordinary internet traffic. The very last address, 255.255.255.255, is separately used as the broadcast address.

Today, CIDR notation has replaced fixed classes

Modern routers and network equipment no longer use fixed boundaries like Class A, B, or C — instead they use CIDR notation (like /24 or /27), which lets a network's size be set freely rather than restricted to the three fixed sizes classful addressing allowed.

Why the class boundaries wasted so much address space

Because network size under classful addressing could only be one of three fixed sizes (/8, /16, or /24), an organization that needed, say, 2,000 addresses still had to be handed an entire Class B block of 65,534 — a massive waste multiplied across thousands of organizations, and a major reason the system was eventually replaced.

Class D and E rarely come up outside specialized contexts

Unlike Classes A, B, and C, Class D (multicast) and Class E (reserved) are not assigned to everyday devices at all. Class D shows up in things like routing-protocol traffic and video streaming groups, while Class E remains reserved for research and future use and essentially never appears in ordinary internet traffic.

Frequently Asked Questions

Is the class system still used for internet routing today?

No — since 1993, CIDR (Classless Inter-Domain Routing) has been the real-world standard, and actual routing decisions do not consider class boundaries. The term "class" mostly persists as shorthand when explaining private IP ranges or teaching networking basics.

How do I know which class my own IP address belongs to?

Just check the value of the first octet (the first number) of the IP address: 0–127 is Class A, 128–191 is Class B, 192–223 is Class C, 224–239 is Class D, and 240–255 is Class E.