IPv6 Subnet Calculator
Calculate an IPv6 network from an address and a prefix between 0 and 128. The result includes compressed and expanded text, the first and last address, and the exact count. There is no broadcast address and no IPv4-style usable-host subtraction.
What /64 does, and does not, mean
SLAAC and many operator guides assume a /64 on a link. That is a convention for interface identifiers, not a protocol rule that every routed prefix is 64 bits. A /48 or /56 is a common allocation. A /128 is one address.
2001:db8:1:2::1/64 normalizes to 2001:db8:1:2::/64. The block starts at 2001:db8:1:2:: and ends at 2001:db8:1:2:ffff:ffff:ffff:ffff, which is 18,446,744,073,709,551,616 addresses. There is no broadcast to subtract. 2001:db8::/32 is documentation space (RFC 3849), so this example is safe to copy into notes.
Questions
IPv6 does not use a broadcast address. Neighbor discovery uses multicast. The last address in the prefix is just the last address.
It is the loopback address, a single address. Compressing zeros does not change the prefix length.
