Network planning boundaries
IPv6, CIDR and IANA: exact ranges are not routing or service proof
Network arithmetic, registry facts and observed traffic answer different questions. Keep those layers separate before changing a firewall, route or service configuration.
Content updated: · Maintainer and corrections
Use exact counts and explicit normalization
IPv6 uses 128-bit addresses; ordinary floating-point numbers cannot represent every address exactly. A /64 contains 18446744073709551616 mathematical addresses. That is not a count of assignable hosts. IPv6 does not have an IPv4-style broadcast address.
Compressed and expanded forms may name the same address. When host bits are set in a CIDR input, inspect the normalized network prefix. Zone identifiers belong to a scoped host context and are outside these arithmetic inputs; they are not another piece of the address.
Exact aggregation must not add addresses
Union retains every address in either set, intersection retains shared addresses, and subtraction removes only addresses in the second set. Exact CIDR output can merge adjacent aligned blocks only when their complete combined range was already present.
A convenient covering supernet may include addresses outside the inputs. This tool does not silently make that tradeoff. Keep IPv4 and IPv6 operations separate and review empty results, normalization and explicit limits before importing an access list.
Read registry dates, overlapping prefixes and notes
Special-purpose records can overlap; a more specific matching prefix can have different properties. Review the longest match together with broader matches, the original registry attributes, references and footnotes. No match is not a claim that an address is public, safe or globally reachable.
The port registry records service names and transport protocols, not an inventory of a host. A TCP registration does not establish a UDP service or that any process is listening. Both lookups use dated same-origin snapshots; loading a snapshot does not send your search value. They are not live IANA queries or network probes.
Data provenance