IPv6 Subnet & Prefix Calculator
Calculates the normalized IPv6 network, first and last address, and exact decimal address count for one address and prefix.
About this ipv6 subnet & prefix calculator
Calculates the normalized IPv6 network, first and last address, and exact decimal address count for one address and prefix Performs protocol inspection, IP calculation, and network analysis client-side without sending probes or exposing network topology.
Protocol mechanics & network logic
Calculates one IPv6 address range locally. An omitted prefix defaults to /64; a supplied prefix must be an integer from 0 through 128. It returns the compressed address, normalized network, first and last address, and the exact decimal address count.
Worked network diagnostic scenario
Scenario: Calculate exact bounds and count for an IPv6 /64.
Sample input:
Processing: Use BigInt masks for the 64-bit host portion and serialize the exact power-of-two count as decimal text.
Illustrative output:
Addressing limits & protocol boundaries
Only one IPv6 address with an optional /0 through /128 suffix is accepted; an empty suffix or extra slash is rejected. Calculations use BigInt because IPv6 ranges exceed safe JavaScript Number precision, and addressCount is serialized as decimal text. This tool does not allocate prefixes, query a network, inspect routing, or prove address reachability.
Addressing calculations and subnet models in IPv6 Subnet & Prefix Calculator 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 Calculator 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 791 (Internet Protocol: IPv4)
- RFC 4632 (Classless Inter-domain Routing: CIDR)
- RFC 4291 (IP Version 6 Addressing Architecture)
IPv6 Subnet & Prefix Calculator verification · Audit standards
How to use it
- Enter 2001:db8::1/64, or omit the prefix to use /64.
- Click Run locally to validate the IPv6 address and apply the selected prefix.
- Read address, network, firstAddress, lastAddress, prefix, and the exact decimal addressCount fields.
Frequently asked questions
What does the IPv6 calculator return?+
For one IPv6 address and an optional prefix, it returns the compressed address, normalized network, firstAddress, lastAddress, prefix, and exact decimal addressCount.
Can I try a concrete IPv6 example?+
Enter `2001:db8::1/64` and choose Run locally. The network and first address are `2001:db8::`, the last is `2001:db8::ffff:ffff:ffff:ffff`, and addressCount is `18446744073709551616`.
Why is addressCount decimal text?+
Some IPv6 address counts exceed safe JavaScript Number precision, so the tool uses BigInt and serializes the exact count as decimal text.
Which prefixes are accepted?+
The prefix is optional and defaults to `/64`. When supplied it must be an integer from 0 through 128; an empty suffix or extra slash is rejected.