Prefix boundaries are the useful unit
IPv6 design normally revolves around prefixes rather than “usable host counts.” This workbench shows the normalized address, expanded form, network prefix, first/last numerical address, host/interface bits and the number of /64 networks inside a larger allocation.
A /127 is widely used on inter-router point-to-point links, while /128 identifies a single address. IPv6 has no broadcast address.