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IPv6 info: expand, compress, split and convert an address

AdminKit's IPv6 info tool takes a pasted IPv6 address and reports its fully expanded and RFC 5952 compressed canonical forms, its prefix/interface-id split, and its address category -- or takes a MAC address and derives the modified EUI-64 interface id it would produce -- computed entirely offline, with no DNS lookup, geolocation or ownership claim.

Part of the IP & network cluster — more tools, guides and terms on ip & network.

No prefix defaults to a /64 prefix/interface-id split. Paste a MAC address instead to derive the modified EUI-64 interface id it would produce.

Link-local
Compressed form (RFC 5952)
fe80::223:45ff:fe67:89ab
Expanded form
fe80:0000:0000:0000:0223:45ff:fe67:89ab
Prefix (/64)
fe80::/64
Interface id
0223:45ff:fe67:89ab

This interface id is in modified EUI-64 form — the embedded MAC address is 00:23:45:67:89:ab.

Source: RFC 4291 — IP Version 6 Addressing Architecture

What the result means

A link-local or ULA result means the address is not expected to be routable on the public internet by design, not a misconfiguration. An interface id with no embedded MAC usually means the device uses a randomized address rather than modified EUI-64 — the common case on modern operating systems. For the address's broader IANA special-use classification, see IP info instead.

Next step

Need a whole block's range instead of one address? Use the subnet calculator, or look up a MAC's registered vendor next.

Keep this result

Copy a link to this check so you can share it or run it again later. Want a heads-up if something changes? That's early access, not a live feature yet — tell us and we'll set it up by hand.

Get alerted — early access

How it works and limits

Paste a single IPv6 address — with or without a /prefix — and this tool reports its fully expanded 8-group form, its RFC 5952 canonical compressed form, its prefix/interface-id split (defaulting to the conventional /64 boundary), and its address category. If the interface id is in modified EUI-64 form it also shows the MAC address embedded in it; paste a MAC address instead and it derives the modified EUI-64 interface id that MAC would produce. Every result is computed in your browser from the text you paste: no DNS query, no geolocation database, and no claim about who owns or operates the address.

What it reports

  • Expanded and compressed forms — the full 8-group form with every group padded to 4 hex digits, and the RFC 5952 canonical compressed form (lower-case, leading zeros dropped, the longest run of all-zero groups collapsed to ::).
  • Prefix / interface-id split — the address split at a /64 boundary by default (the width SLAAC and modified EUI-64 both use for the interface id), or at whatever /N you append to the address instead.
  • Address category — RFC 4291’s loopback (::1), unspecified (::) and link-local (fe80::/10) ranges; unique local address / ULA (fc00::/7, RFC 4193); multicast (ff00::/8); the 2001:db8::/32 documentation range (RFC 3849); or, matching none of these, global unicast — ordinarily routable on the public internet, though this tool has no way to confirm anyone actually announces a route for it.
  • Embedded MAC / EUI-64 conversion, both directions — when a /64 interface id carries the ff:fe marker modified EUI-64 inserts, the embedded MAC is extracted; paste a MAC address instead and the tool derives the modified EUI-64 interface id it would produce, by the same RFC 4291 process in reverse.

Reading the result

A link-local or ULA result means the address is not expected to be routable on the public internet by design, not a misconfiguration. A global unicast result only means the address sits outside every range this tool checks; it is not proof the address is currently assigned, reachable, or safe. An interface id with no embedded MAC usually means the device uses a randomized address (IPv6 Privacy Extensions, RFC 8981) rather than modified EUI-64 — that is the common case on modern operating systems, not an error. For a single address’s broader IANA special-use classification (including IPv4), see IP info instead; for a whole CIDR block’s network/broadcast/host-range math, see the subnet calculator.

Limits

  • No DNS, WHOIS, geolocation or ASN lookups are performed, ever — this is pure arithmetic over the address’s (or MAC’s) own bits.
  • EUI-64 extraction only runs on a /64 split, since the modified EUI-64 format is defined as exactly 64 bits wide; a custom /N split still reports the prefix and interface id, just without attempting MAC extraction.
  • A single address only — for a CIDR block’s full address range, see the subnet calculator instead. For a MAC’s registered manufacturer rather than its derived IPv6 interface id, see MAC vendor lookup.

See EUI-64 and link-local address for more on two of the concepts this tool works with.

Frequently asked questions

Does this tool look up the address over DNS, or say who owns it?

No -- it never performs a DNS query and makes no ownership, ASN or ISP claim. It only reformats and classifies the address you paste: its expanded and compressed forms, its prefix/interface-id split, its address category, and whether the interface id embeds a MAC address.

What does it mean for an interface id to be in "modified EUI-64 form"?

Modified EUI-64 (RFC 4291, using the identifier format RFC 7042 maintains) splits a 48-bit MAC address in half, inserts the fixed value fffe in the middle, and flips the universal/local bit of the first octet, producing a 64-bit interface id that embeds the original MAC. This tool checks for that ff:fe marker and, when it finds one, reverses the process to show the embedded MAC.

Why does the prefix/interface-id split default to /64 if I don't specify a prefix length?

Because /64 is the conventional boundary IPv6 autoconfiguration (SLAAC) and modified EUI-64 both use for the interface id -- pasting a plain address with no "/N" suffix assumes that common case. Add your own "/N" (e.g. /48) to split at a different boundary instead; outside a /64 split, no EUI-64 extraction is attempted, since that format is only ever 64 bits wide.

Why doesn't every address have an embedded MAC I can extract?

Modern operating systems generate a randomized interface id by default (IPv6 Privacy Extensions, RFC 8981) specifically so the device's MAC can't be read back out of its address -- an interface id without the ff:fe marker in the middle simply wasn't built from a MAC in the first place, whether randomized or manually assigned.