Subnet and CIDR calculator

Normalize a prefix, inspect its address boundaries and copy the result. Calculating a block does not perform an IP lookup.

Try an example8.8.8.9/24 192.0.2.1/31 0.0.0.0/0 2001:db8::1/64 ::/128

2001:db8::/64

Normalized IPv6 network

64 network bits64 host bits

IPv6 has 128 bits. The prefix fixes 64; 64 remain for addresses in the block.

First address: 2001:db8::
Last address: 2001:db8::ffff:ffff:ffff:ffff

Total addresses: Exact addresses18,446,744,073,709,551,616Mathematical block size. Not observed hosts or database coverage.
Prefix length: /64

IPv6 prefix details

Network bits: 64
Address bits after the prefix: 64
/64 subnets in this block: 1

IPv6 has no broadcast address. Address-space counts do not measure assigned devices or available interface identifiers.

Look up first address

No published network profile is available for this exact CIDR. The boundary calculation is still valid.

Reading the calculation

The prefix fixes the network bits. The remaining n bits give 2^n addresses. This is the size of the block, not an allocation, announced route or count of active devices.

IPv4 /31 point-to-point links use both addresses; a /32 identifies one address. IPv6 has no broadcast address. Documentation blocks such as 192.0.2.0/24 and 2001:db8::/32 do not imply public routability.

CIDR explained IPv6 address lookup IPv4 /31 rules IPv6 addressing