IPv6 Subnet Calculator
Expand and compress IPv6 addresses, detect their type, and get the network, first and last address plus exact 128-bit address counts. Split subnets by prefix and build EUI-64 interface IDs from a MAC — all offline in your browser.
What does the IPv6 subnet calculator show?
For any address and prefix it displays the fully expanded form, the RFC 5952 compressed form, the address type, the network address, the first and last address of the subnet, and the exact number of addresses it contains.
How does the compressed form work?
The tool follows RFC 5952: one longest run of zero groups is replaced by a double colon, hexadecimal letters are lower-case and leading zeros inside a group are removed, for example 2001:0db8:0000:0000:0000:0000:0000:0001 becomes 2001:db8::1.
Which address types are detected?
Global unicast (2000::/3), link-local (fe80::/10), unique local addresses (fc00::/7), multicast (ff00::/8), plus the special loopback ::1, unspecified ::, IPv4-mapped ::ffff:0:0/96 and the documentation range 2001:db8::/32.
Why does it use BigInt arithmetic?
An IPv6 subnet can hold up to 2 to the power of 128 addresses, a number far beyond the precision of normal JavaScript numbers. Exact 128-bit integer math guarantees the totals, network and boundary addresses are always correct, and huge counts are also shown in scientific notation.
How does subnet splitting work?
Enter a new prefix length larger than the current one. The calculator reports how many equal-sized subnets the range splits into (2 to the power of the difference) and lists the network address of the first eight of them.
What is EUI-64 and how is it used here?
EUI-64 builds a 64-bit interface ID from a MAC address by inserting ff-fe in the middle and flipping the seventh bit. Paste a MAC to see the interface ID, the matching fe80:: link-local address and the same ID combined with your current prefix.
Is the first address in a subnet usable?
Yes. Unlike IPv4, IPv6 has no broadcast address, so the network address itself is assignable. The last address of the range is equally usable, which is why the tool shows first and last as regular host addresses.
Does anything get sent over the network?
No. All parsing and arithmetic runs locally in your browser with exact 128-bit integers. Addresses, prefixes and MAC inputs never leave your device and no account is required.
How to Use IPv6 Subnet Calculator
This calculator takes any IPv6 address with its prefix length and shows everything worth knowing about the subnet: the fully expanded form, the RFC 5952 compressed form, the address type, the network address, the first and last address, and the exact number of addresses — computed with 128-bit BigInt math so even a /0 total is exact. You can also split the subnet into smaller ones by a new prefix and derive an EUI-64 interface ID from a MAC address. Everything runs locally in your browser.
- Type an IPv6 address such as 2001:db8:85a3::8a2e:370:7334 — you may include the prefix directly (2001:db8::/32) and the prefix field fills itself.
- Set or confirm the prefix length (0–128); results update live as you type.
- Read the cards: expanded and compressed forms, address type, network, first and last address, and the total with exact digits plus scientific notation.
- To slice the range, enter a larger New prefix in the Split box — you get the subnet count and the network addresses of the first eight subnets.
- Optionally paste a MAC address to get its EUI-64 interface ID, the matching fe80:: link-local address and the ID combined with your prefix, or press Random IID for a locally administered random identifier.
In IPv6 the network address is a usable host address (there is no broadcast), so First address equals the network address. The compressed form always follows RFC 5952: lower-case hex, no leading zeros, and exactly one :: for the longest zero run.
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