IPv6 subnet allocation planner calculator

A prefix determines an exact address count

IPv6 blocks can exceed the exact-integer capacity of ordinary floating-point numbers. This page uses 128-bit integer arithmetic and displays counts as decimal text.

The first and last addresses describe arithmetic endpoints. They do not establish which addresses a network policy or device configuration can assign.

The ipv4 vlsm subnet planner calculator adds plan largest-first variable IPv4 subnet blocks from host demands, with exact alignment, explicit /31 and /32 interpretation and remaining CIDRs.

Largest-first requests avoid silent fragmentation

Requests are ordered by descending block size, with input order preserved for equal sizes. Every allocated start is aligned to the child’s size and stays within the parent.

All requested children must fit. The tool reports an input error rather than silently dropping a request and presenting a partial plan as complete.

Canonical text is a representation rule

Output uses lowercase hexadecimal and compresses the leftmost longest qualifying zero run. A shorter string does not change the underlying 128-bit address.

The normalized parent is displayed explicitly when entered host bits are cleared. Remaining space is decomposed into aligned CIDRs, rather than reported as an arbitrary unaligned address interval only.

Use the result with the next measurement

The IPv4 VLSM subnet planner calculator converts host demands into IPv4 blocks under an explicit reserved-address convention. IPv6 prefix allocation does not reuse its broadcast rules.

Offline arithmetic, not scanning, reachability or assignment permission. Pure hexadecimal notation only; no embedded dotted IPv4 or zone identifiers. No IPv6 broadcast subtraction.