How this calculation works
Translate each demand into a block under the chosen host convention, sort largest first and allocate aligned subnet ranges inside the normalized parent. Report exact unused suffix CIDRs.
Standard block = smallest power of two at least host demand + 2; point-link convention permits /31 for two and /32 for oneA worked example
Within 192.0.2.0/24, fifty standard candidate hosts need /26 and twenty need /27. The blocks begin at 192.0.2.0 and 192.0.2.64, leaving 160 addresses after the two allocations.
Good to know
Arithmetic only, not public routing, DHCP availability or device support. Standard convention reserves network and broadcast; point-link interpretation must fit the actual link. No packets are sent.
Reference: IETF RFC 3021: 31-bit point-to-point prefixes (opens in a new tab) ↗
Host demand is different from total addresses
Under standard subnet interpretation, candidate hosts exclude the network and directed broadcast addresses. The smallest fitting power-of-two block therefore includes two reserved addresses.
The point-link option treats one- and two-address demands differently. It is an explicit supported interpretation, not a claim that every interface can use every /31 or /32 as a conventional LAN.
The ipv6 subnet allocation planner calculator adds allocate aligned IPv6 child prefixes largest first with exact 128-bit arithmetic, canonical ranges and a CIDR decomposition of the remaining suffix.
Keep alignment inside the parent
A block start must be a multiple of its size. Simply adding the requested host count to the previous address would produce overlapping or unaligned CIDR ranges.
The planner normalizes entered parent host bits and shows that normalized block. Oversized request sets are rejected rather than extending into neighboring address space.
Unused addresses are not automatically available infrastructure
Remaining suffix CIDRs state the exact arithmetic remainder after allocation. They do not prove ownership, reachability, lack of DHCP reservations or freedom from special-purpose restrictions.
The example uses documentation address space. Use a parent block appropriate for your own network plan and separately validate real configuration and routing requirements.
Use the result with the next measurement
The IPv6 subnet allocation planner calculator accepts child prefix lengths directly and uses a 128-bit address space. Its candidate endpoints do not require IPv4 network/broadcast subtraction.
Arithmetic only, not public routing, DHCP availability or device support. Standard convention reserves network and broadcast; point-link interpretation must fit the actual link. No packets are sent.
A few questions, answered
Does host count include network and broadcast?
Not in standard mode; those are reserved.
Can point mode allocate one address?
Yes, as an explicit /32 interpretation.
Are incomplete allocations returned?
No, every request must fit or the plan reports an error.