Convert any CIDR block to its start and end IP addresses.
Enter a CIDR block like 192.168.1.0/24 or 2001:db8::/32 to see the full IP range it covers. The tool calculates the first address, last address, and total number of IPs in the block for both IPv4 and IPv6 networks.
CIDR (Classless Inter-Domain Routing) notation is a compact way to describe a block of IP addresses. It combines a network address with a prefix length separated by a slash - for example, 10.0.0.0/8 represents all addresses from 10.0.0.0 to 10.255.255.255. The prefix length indicates how many leading bits define the network portion of the address.
CIDR replaced the older classful addressing system and is used everywhere in networking - from firewall rules and routing tables to cloud security groups and access control lists. A /24 block contains 256 IPv4 addresses, a /16 contains 65,536, and a /8 contains over 16 million. IPv6 CIDR blocks can be vastly larger, with a /64 containing 2^64 addresses.