CIDR

CIDR writes a network as an address and a prefix length: how many bits are the network. A /24 is 256 IPv4 addresses, minus the usual network and broadcast caveats. A /32 is one host. IPv6 uses the same idea with larger numbers.

Overlapping routes follow longest match. A too-wide allow-list in a firewall is how you meant /32 and shipped /16. Inventory your prefixes. Do not describe allocations as class A, B, or C unless you enjoy being wrong in meetings.