Expand, compress, and derive the reverse-DNS of any IPv6 address.
Tip: use samples, upload, copy, download, and send-to actions inside the workspace where available.
IPv6 Calculator is a free, browser-based tool that helps you get the job done quickly. Expand, compress, and derive the reverse-DNS of any IPv6 address. It's built for speed and privacy: Everything runs locally in your browser — your data is never uploaded to a server. No sign-up, no installs, and no daily limits.
Use this tool as the focused step in a larger browser-based workflow.
Review the preview, copy or download the result, and keep everything local in your browser.
IPv4 Subnet Calculator: Network, broadcast, host range, mask, and class from an IP + prefix.
Open toolCIDR Calculator: Turn a CIDR block into its address range, mask, and host count.
Open toolSubnet Calculator: Plan subnets: network, usable range, broadcast, and mask.
Open toolThe prefix keeps the leading 64 bits and zeroes the remaining 64, giving the network address. Setting all 64 host bits produces the last address — IPv6 has no broadcast address, so both ends of the range are usable. Compression removes leading zeros in each group and replaces the single longest run of all-zero groups with ::; only one such run may be elided, which is why an address has exactly one canonical compressed form (RFC 5952).
2001:db8::/32 is reserved for docs and examples.
Blue groups are entirely inside the /64 network portion, amber is the group the prefix boundary cuts through, grey is host space. A /48 is a common site allocation, /56 a common residential delegation, and /64 the standard single-subnet size because SLAAC needs 64 host bits to build interface identifiers.
| # | Subnet | First address | Last address | |
|---|---|---|---|---|
| 1 | 2001:db8::/64 | 2001:db8:: | 2001:db8::ffff:ffff:ffff:ffff |
Borrowing 0 bits yields 20 = 1 subnets of /64. Only the first 1 are listed; each successive network address increases by 264.
The reverse-DNS name reverses all 32 nibbles of the expanded address and joins them with dots under ip6.arpa — this is what a PTR record is keyed on, so it must always be built from the fully expanded form, never the compressed one.
Modified EUI-64 splits the MAC in half, inserts ff:fe between the two halves, and inverts the universal/local bit (bit 1 of the first byte) — so 00:… becomes 02:…. Prefixing fe80::/64 gives the link-local address the interface configures itself. Because this embeds the hardware address, most modern stacks prefer RFC 8981 temporary random identifiers for outbound traffic instead.
