What is an IP address class checker?
An IP address class checker identifies the traditional class of an IPv4 address based primarily on its first octet. Under the original classful addressing system, IPv4 addresses were grouped into Class A, Class B, Class C, Class D and Class E ranges.
The checker can also identify whether an address belongs to a common private IPv4 range or a special-use range such as loopback, link-local or multicast space.
What are IPv4 address classes?
IPv4 address classes were part of the original classful networking system. The first few bits of an address determined the class, which in turn determined the default network size.
Class A networks were designed for very large networks, Class B for medium-sized networks and Class C for smaller networks. Class D was reserved for multicast traffic, while Class E was set aside for experimental or special purposes.
IPv4 class ranges
| Class | First Octet | Traditional Range | Default Mask | Default Prefix |
|---|---|---|---|---|
| Class A | 1–126 | 1.0.0.0 – 126.255.255.255 | 255.0.0.0 | /8 |
| Class B | 128–191 | 128.0.0.0 – 191.255.255.255 | 255.255.0.0 | /16 |
| Class C | 192–223 | 192.0.0.0 – 223.255.255.255 | 255.255.255.0 | /24 |
| Class D | 224–239 | 224.0.0.0 – 239.255.255.255 | N/A | N/A |
| Class E | 240–255 | 240.0.0.0 – 255.255.255.255 | N/A | N/A |
Classful addressing is largely historical. Modern networks generally use CIDR notation rather than fixed Class A, B and C boundaries.
What is a Class A IP address?
A traditional Class A address has a first octet from 1 through 126. Its default subnet mask is 255.0.0.0, equivalent to a /8 prefix. Class A networks were designed to provide a very large host address space.
What is a Class B IP address?
A traditional Class B address begins with a first octet from 128 through 191. Its default subnet mask is 255.255.0.0, equivalent to /16.
What is a Class C IP address?
A traditional Class C address begins with a first octet from 192 through 223. Its default subnet mask is 255.255.255.0, equivalent to /24.
The familiar private range 192.168.x.x falls within the historical Class C address space, although modern networks use CIDR rather than classful addressing for subnet boundaries.
What are Class D and Class E addresses?
Class D covers addresses beginning from 224 through 239 and is associated with IPv4 multicast. These addresses do not use a traditional Class A, B or C host/network structure.
Class E traditionally covers addresses beginning from 240 through 255 and has been reserved for experimental or special-use purposes.
Private vs public IPv4 addresses
Private IPv4 addresses are intended for use inside local networks. They are commonly used by homes, businesses, data centers and internal systems and are not directly routed on the public Internet.
| Private IPv4 Range | CIDR |
|---|---|
| 10.0.0.0 – 10.255.255.255 | 10.0.0.0/8 |
| 172.16.0.0 – 172.31.255.255 | 172.16.0.0/12 |
| 192.168.0.0 – 192.168.255.255 | 192.168.0.0/16 |
What about 127.x.x.x?
Addresses in 127.0.0.0/8 are reserved for loopback communication. The most familiar example is 127.0.0.1, commonly called localhost. Traffic sent to a loopback address remains on the local device.
What is a link-local IPv4 address?
IPv4 addresses in 169.254.0.0/16 are link-local addresses. They may be assigned automatically when a device cannot obtain a normal IPv4 configuration from a DHCP server.
Do IP address classes still matter?
IP address classes are useful for understanding the history and fundamentals of IPv4 networking, but modern network design generally uses CIDR rather than the original fixed Class A, B and C boundaries.
With CIDR, a network can use prefixes such as /20, /23, /27 or /30 without being limited to the traditional class default masks. This allows IPv4 address space to be allocated much more efficiently.
Frequently asked questions
What class is 192.168.1.1?
192.168.1.1 falls within the historical Class C range because its first octet is 192. It is also a private IPv4 address.
What class is 10.0.0.1?
10.0.0.1 is historically a Class A address because its first octet is 10. It also belongs to the private 10.0.0.0/8 address block.
What class is 172.16.0.1?
172.16.0.1 falls within the historical Class B range and is also inside the private 172.16.0.0/12 block.
What is the default subnet mask for Class C?
The traditional default Class C subnet mask is 255.255.255.0, equivalent to CIDR prefix /24.
Is 127.0.0.1 a Class A address?
The first octet falls numerically near the Class A range, but 127.0.0.0/8 is reserved for loopback use and should be treated as special-use addressing rather than a normal Class A network.
Are Class A, B and C still used for subnetting?
Modern IPv4 networks use CIDR prefixes rather than relying on fixed class boundaries. Class terminology is now mainly useful for historical understanding, education and quick identification.