IPv4 Classes & Ranges
IPv4 Classes & Ranges
Classful IPv4 addressing (now largely historical but still taught) divides the 32-bit IPv4 space into five classes (A to E), defined by the leading bits and default network/host boundaries.
Class A IPv4 Range
- Leading bits: 0
- First octet range: 0–127
- Default mask: /8 (255.0.0.0)
- Networks: 128 networks (0.0.0.0 to 127.0.0.0), each with up to ~16.7 million hosts
- Typical use: Very large networks
- Private range (Class A-sized): 10.0.0.0/8
Class B IPv4 Range
- Leading bits: 10
- First octet range: 128–191
- Default mask: /16 (255.255.0.0)
- Networks: 16,384 networks, each with up to ~65,534 hosts
- Typical use: Medium-sized networks
- Private range (Class B-sized): 172.16.0.0/12 (172.16.0.0–172.31.255.255)
Class C IPv4 Range
- Leading bits: 110
- First octet range: 192–223
- Default mask: /24 (255.255.255.0)
- Networks: ~2,097,152 networks, each with up to 254 hosts
- Typical use: Small networks
- Private range (Class C-sized): 192.168.0.0/16 (commonly used as /24s)
Class D (Multicast) IPv4 Range
- Leading bits: 1110
- First octet range: 224–239
- Purpose: IP multicast groups, not unicast hosts
- Not subnetted by classful masks; uses group IDs
Class E (Experimental) IPv4 Range
- Leading bits: 1111
- First octet range: 240–255
- Purpose: Reserved/experimental; not for general use
Well-Known Special Ranges (within or across classes) IPv4 Range
- Private addressing (not routed on the public Internet): 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16
- Loopback:127.0.0.0/8 (commonly 127.0.0.1)
- Link-Local (APIPA):169.254.0.0/16 for auto configuration
- Multicast:224.0.0.0/4 (includes 224.0.0.0–239.255.255.255). Local subnet scope examples: 224.0.0.1 (all hosts), 224.0.0.2 (all routers)
- Broadcast:255.255.255.255 (limited broadcast), and subnet-directed broadcasts (a network’s host bits all 1s)
- Carrier-grade NAT:100.64.0.0/10
