Special IPv4 addresses are reserved for specific purposes and cannot be used as normal host addresses.
Network address
- Identifies the subnet itself – cannot be assigned to a host
- All host bits = 0
- Example: 192.168.1.0/24
Broadcast address
- Sends traffic to all hosts in the subnet
- All host bits = 1
- Example: 192.168.1.255/24
Loopback
- Tests the local TCP/IP stack
127.0.0.0/8, most used: 127.0.0.1- Router loopbacks are often used as Router-ID (OSPF/BGP)
APIPA
- Automatic address when DHCP fails (Windows feature)
- Range:
169.254.0.0/16 - Link-local only – no default gateway
Quick table
| Type | Range | Routable |
|---|---|---|
| Network | Host bits = 0 | ❌ |
| Broadcast | Host bits = 1 | ❌ |
| Loopback | 127.0.0.0/8 | ❌ |
| APIPA | 169.254.0.0/16 | ❌ |
Exam tips ⚠️
- See 169.254.x.x → DHCP problem
- Network + broadcast are never host addresses
- Loopback ≠ local LAN address