CIDR notation expresses IP ranges as address/prefix: 192.168.1.0/24 = 256 addresses (254 usable). /24 = 255.255.255.0 mask. /25 = 128 addresses, /26 = 64, /30 = 4 (2 usable).
Memorize common prefixes: /8=16M hosts, /16=65K hosts, /24=254 hosts, /25=126, /26=62, /27=30, /28=14, /29=6, /30=2. Calculate: hosts = 2^(32-prefix) - 2. /30 is ideal for point-to-point links.