Subnet calculator
Enter an address with a prefix (192.168.1.10/24 or 2001:db8::1/64), or an address and a netmask separated by a space.
The calculator shows the network address, broadcast address, first and last host, number of addresses, netmask and wildcard mask. For IPv6 it prints the compressed and expanded forms, network boundaries and the ip6.arpa reverse record.
The prefix (/24, /64) is the number of one-bits in the mask: the larger the prefix, the smaller the network. An IPv4 /24 has 254 host addresses because the first address is the network and the last is broadcast. /31 and /32 networks are exceptions.