IP Address Class Finder — Identify IPv4 Class, Type and Range

Our free IP address class finder instantly identifies the class (A, B, C, D or E), default subnet mask, address range, private/public status and any special designation (loopback, APIPA, multicast) of any IPv4 address. Essential for networking students studying for CCNA and CompTIA Network+ and for engineers quickly classifying unfamiliar IP addresses.

IPv4 Address Classes Explained

The original IPv4 addressing scheme divided the 32-bit address space into classes based on the first octet. While modern networks use CIDR (classless routing) and the class system is largely historical, understanding classes remains essential for exam success and interpreting legacy documentation.

• Class A (1–126.x.x.x) — First bit is 0. Default mask /8 (255.0.0.0). 126 networks, 16 million hosts each. Assigned to large organisations and governments. 127.x.x.x is reserved for loopback.
• Class B (128–191.x.x.x) — First two bits are 10. Default mask /16 (255.255.0.0). 16,384 networks, 65,534 hosts each. Used by universities and large enterprises.
• Class C (192–223.x.x.x) — First three bits are 110. Default mask /24 (255.255.255.0). 2 million networks, 254 hosts each. Most common for small networks.
• Class D (224–239.x.x.x) — First four bits are 1110. Reserved for multicast groups. Not assigned to individual hosts.
• Class E (240–255.x.x.x) — Reserved for experimental use. Not used in production networks.

Special IPv4 Addresses to Know

• 127.0.0.1 — Loopback address. Packets never leave the host. Used for local testing.
• 0.0.0.0 — "This network". Used in routing as the default route.
• 169.254.x.x — APIPA (Automatic Private IP Addressing). Assigned automatically when DHCP fails. Indicates a DHCP problem.
• 255.255.255.255 — Limited broadcast. Sent to all hosts on the local network segment.
• RFC 1918 private ranges — 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16 — not routable on the public internet.