Lesson 13: IPv4 Address Classes
Historically, IPv4 addresses were categorized into classes based on the value of the first octet.
IP Address Classes (Classful Addressing)
| Class | First Octet Range | Default Mask (CIDR) | Purpose |
|---|---|---|---|
| A | 1 – 126 | 255.0.0.0 (/8) | Large networks (few networks, many hosts) |
| B | 128 – 191 | 255.255.0.0 (/16) | Medium networks |
| C | 192 – 223 | 255.255.255.0 (/24) | Small networks (many networks, few hosts) |
| D | 224 – 239 | N/A | Multicast (one-to-many) |
| E | 240 – 255 | N/A | Reserved/Experimental |
(Note: 127.x.x.x is reserved for loopback testing.)
Special/Reserved IPv4 Addresses
- Network Address: The first address in any subnet, where the host portion is all 0s. Cannot be assigned to a device.
- Broadcast Address: The last address in any subnet, where the host portion is all 1s. Used to send data to all devices on that segment.
- Loopback (127.0.0.1): Used for testing TCP/IP stack functionality on a local machine.
- Link-Local (APIPA): Addresses in the
169.254.0.0/16range. Automatically assigned when a device fails to get a DHCP address.