As of the writing of this reference, this is the most widely used IP version. It consists of four numbers separated by periods (e.g., 192.168.0.1), with each number ranging from 0 to 255. IPv4 addresses are 32-bit numbers, allowing for about 4.3 billion unique addresses.
The Five IPv4 Classes – Quick Reference
IPv4 addresses are categorized into five classes: A, B, C, D, and E. Each class is designed to accommodate different sizes and types of networks. The classes differ primarily by the size of the network and host portions of the address.
IPv4 Address Classes with Public and Private Ranges
| Class | Public IP Range | Private IP Range | Default Subnet Mask | Number of Networks | Number of Hosts per Network | Purpose |
|---|---|---|---|---|---|---|
| A | 1.0.0.0 – 126.255.255.255 | 10.0.0.0 – 10.255.255.255 | 255.0.0.0 | 128 | 16,777,214 | Very large networks |
| B | 128.1.0.0 – 191.255.255.255 | 172.16.0.0 – 172.31.255.255 | 255.255.0.0 | 16,384 | 65,534 | Medium-sized networks |
| C | 192.0.1.0 – 223.255.254.255 | 192.168.0.0 – 192.168.255.255 | 255.255.255.0 | 2,097,152 | 254 | Small-sized networks |
| D | 224.0.0.0 – 239.255.255.255 | N/A | N/A | N/A | N/A | Multicast groups |
| E | 240.0.0.0 – 255.255.255.255 | N/A | N/A | N/A | N/A | Experimental, future use |
Special Address Ranges
| Type | Range | Purpose |
|---|---|---|
| Loopback | 127.0.0.0 – 127.255.255.255 | Loopback testing |
| Link-Local | 169.254.0.0 – 169.254.255.255 | Automatic private IP addressing (APIPA) |
Class A
- Range: 0.0.0.0 to 127.255.255.255
- Default Subnet Mask: 255.0.0.0
- Number of Networks: 128 (2^7, with the first bit set to 0)
- Number of Hosts per Network: 16,777,214 (2^24 – 2)
- Purpose: Designed for very large networks (e.g., large corporations or ISPs).
Class B
- Range: 128.0.0.0 to 191.255.255.255
- Default Subnet Mask: 255.255.0.0
- Number of Networks: 16,384 (2^14, with the first two bits set to 10)
- Number of Hosts per Network: 65,534 (2^16 – 2)
- Purpose: Designed for medium-sized networks (e.g., universities, large businesses).
Class C
- Range: 192.0.0.0 to 223.255.255.255
- Default Subnet Mask: 255.255.255.0
- Number of Networks: 2,097,152 (2^21, with the first three bits set to 110)
- Number of Hosts per Network: 254 (2^8 – 2)
- Purpose: Designed for small-sized networks (e.g., small businesses, small ISPs).
Class D
- Range: 224.0.0.0 to 239.255.255.255
- Purpose: Reserved for multicast groups. These addresses are not assigned to individual hosts but to multicast groups for delivering messages to multiple destinations.
Class E
- Range: 240.0.0.0 to 255.255.255.255
- Purpose: Reserved for experimental use and future development. These addresses are not used in regular network operations.
Special Address Ranges
- Loopback Addresses: 127.0.0.0 to 127.255.255.255 (Typically 127.0.0.1 is used for loopback testing)
- Private Addresses: These are used within private networks and are not routable on the internet.
- Class A: 10.0.0.0 to 10.255.255.255
- Class B: 172.16.0.0 to 172.31.255.255
- Class C: 192.168.0.0 to 192.168.255.255
These classes and ranges help organize IP addressing and ensure that devices within different types of networks can communicate effectively.