IPv6 Subnet & Prefix Allocation Planner
Plan IPv6 subnet depth with exact BigInt capacity, compressed and full first/last addresses, a 128-bit split diagram and bounded pages.
About this ipv6 subnet & prefix allocation planner
Plan IPv6 subnet depth with exact BigInt capacity, compressed and full first/last addresses, a 128-bit split diagram and bounded pages Performs protocol inspection, IP calculation, and network analysis client-side without sending probes or exposing network topology.
Protocol mechanics & network logic
Enter an IPv6 CIDR and a target prefix length from the parent length through 128. Calculate, browse 16 subnets per page, or jump to a zero-based page number. Editing a parameter clears the previous result. The existing requested-count calculator remains below.
Worked network diagnostic scenario
Scenario: Divide one documentation IPv6 /56 into four equal local prefixes.
Sample input:
Processing: Borrow two bits and enumerate the first four /58 prefix starts. 2001:db8::/32 divided at /48 gives 65536 subnets, each with 1208925819614629174706176 addresses. First: 2001:db8::/48; last: 2001:db8:ffff::/48.
Illustrative output:
Addressing limits & protocol boundaries
The tool borrows enough bits for the next power of two but returns only the requested first N subnets. For /56 with count 4 it borrows 2 bits and returns four /58 prefixes: 2001:db8:1000::/58, 2001:db8:1000:40::/58, 2001:db8:1000:80::/58 and 2001:db8:1000:c0::/58. A count of 3 also uses two borrowed bits and leaves one possible /58 unlisted. Offline address arithmetic only. Host bits in the input are masked. All numerical subnet and page counts remain exact up to 2^128; only 16 rows are materialized per page. Address counts include every bit pattern and are not promises of usable hosts, routing suitability or configuration. The separate count calculator retains its 1–65536 count limit.
Addressing calculations and subnet models in IPv6 Subnet & Prefix Allocation Planner follow IETF RFC definitions. Ensure subnet masks and CIDR prefixes match your network topology.
Offline network inspection boundary
Address parsing and CIDR calculations in IPv6 Subnet & Prefix Allocation Planner run entirely client-side without probing external IP networks or transmitting routing data.
IETF RFC specifications & IANA registries
IETF Request for Comments (RFC) standards and IANA registry references:
- RFC 4291 (IP Version 6 Addressing Architecture)
- RFC 4007 (IPv6 Scoped Address Architecture; scope context only)
IPv6 Subnet & Prefix Allocation Planner verification · Audit standards
How to use it
- Enter, paste, or select your input data into the IPv6 Subnet & Prefix Allocation Planner workspace controls.
- Review parameter fields, units, or options configured for IPv6 Subnet & Prefix Allocation Planner.
- Click the action button or observe immediate live calculations rendered by IPv6 Subnet & Prefix Allocation Planner.
Frequently asked questions
What does the IPv6 planner calculate?+
It accepts CIDR text or JSON containing cidr and subnets/count. It masks the address to the allocated prefix, borrows ceil(log2(requestedSubnets)) bits, and emits exactly the requested number of equally sized subnet prefixes from the start of that allocation. It does not allocate addresses on a network.
Which inputs and limits apply?+
The requested count must be an integer from 1 through 65536. The prefix must be an integer from 0 through 128 and the computed subnet prefix cannot exceed 128. JSON uses cidr or prefix plus subnets or count; plain CIDR defaults to two subnets. Invalid JSON, a non-IPv6 address, invalid prefix, count, or exhausted space produces an error.
How are non-power-of-two counts handled?+
For /56 with count 4 it borrows 2 bits and returns four /58 prefixes: 2001:db8:1000::/58, :40::/58, :80::/58 and :c0::/58.
What result does the worked example produce?+
For 2001:db8:1000::/56 with four requested subnets, the output is 2001:db8:1000::/58, 2001:db8:1000:40::/58, 2001:db8:1000:80::/58 and 2001:db8:1000:c0::/58. This is a local calculation; it does not configure a router or allocate addresses on a network.