Show the first and last address inside an IPv6 prefix along with the size of the address space it covers.
Clearing every host bit gives the first address; setting them all gives the last. Because IPv6 has no broadcast address, both ends of the range are usable, although the all-zeros address is reserved as the subnet-router anycast address. Explicit bounds are what you paste into firewall objects and DDoS scrubbing policies, and they make it obvious when two prefixes overlap.
IPv6 Host Range
first = address AND mask, last = first OR NOT(mask), count = 2^(128 − prefix).
first = address AND mask, last = first OR NOT(mask), count = 2^(128 − prefix). Clearing every host bit gives the first address; setting them all gives the last. Because IPv6 has no broadcast address, both ends of the range are usable, although the all-zeros address is reserved as the subnet-router anycast address.
Explicit bounds are what you paste into firewall objects and DDoS scrubbing policies, and they make it obvious when two prefixes overlap.
This calculator takes 2 inputs: IPv6 address, Prefix length. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.