Lesson 32: IPv4 Address Structure and Classes
The current dominant version of the Internet Protocol is IPv4 (version 4). We will focus heavily on IPv4 addressing before moving to IPv6.
IPv4 Address Format
An IPv4 address is a 32-bit binary number. For ease of use, it is represented in dotted-decimal notation.
- The 32 bits are divided into four groups of 8 bits (called octets).
- Each octet is converted from binary to a decimal number, separated by dots (e.g.,
192.168.1.1). - The decimal value of an octet can range from 0 to 255 (since 8 bits can represent 2^8 = 256 values).
Historical IP Addressing Classes (Classful)
Historically, IP addresses were categorized into five classes based on the value of the first octet. This system defined the split between the Network portion and the Host portion of the address.
| Class | Range of First Octet | Network/Host Split | Purpose |
|---|---|---|---|
| Class A | 1 to 126 | N.H.H.H | Huge networks (large organizations) |
| Class B | 128 to 191 | N.N.H.H | Mid-sized networks (universities) |
| Class C | 192 to 223 | N.N.N.H | Small networks (standard LANs) |
| Class D | 224 to 239 | Reserved | Multicasting |
| Class E | 240 to 255 | Reserved | Experimental |
Note: We no longer use this rigid class system (we use CIDR, Lesson 37), but understanding these classes is vital for historical context and recognizing default ranges.