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MtrXTools

IPv6 tools

Expand or compress an IPv6 address (RFC 5952), see its type, decode embedded IPv4 (6to4, Teredo, NAT64, mapped), recover the MAC from an EUI-64 address, build one from a MAC, and get the ip6.arpa reverse zone. Runs in your browser.

What it works out

  • Canonical form: the RFC 5952 text (lower case, the longest run of zero groups as ::) and the full 32-digit form.
  • Address type: global unicast, unique local, link-local, multicast with its scope, documentation, loopback, 6to4, Teredo, NAT64 and the deprecated ranges.
  • Embedded IPv4: the gateway in a 6to4 address, the server, client address and port in a Teredo address, and the IPv4 address inside NAT64 and IPv4-mapped addresses.
  • EUI-64: when the interface identifier contains ff:fe, the MAC address it was built from, and the reverse: build the link-local or global address from a MAC.
  • Reverse DNS: the ip6.arpa PTR name for an address, and the reverse zone for a prefix. A prefix that isn't a multiple of 4 bits needs several zones, which are listed.
  • The solicited-node multicast address Neighbor Discovery uses for the address.

Why the short form matters

The same IPv6 address can be written many ways: 2001:0DB8:0:0::1, 2001:db8::0:1 and 2001:db8::1 are identical. RFC 5952 defines one canonical form so logs, configs and certificates can be compared as text. Use it in allow-lists and documentation.

Questions

How do I expand a compressed IPv6 address?
Replace :: with as many groups of 0000 as are needed to make eight groups, then pad every group to four hex digits. The tool shows the result as "Expanded".
Does my IPv6 address reveal my MAC address?
Only if the interface identifier is a modified EUI-64, recognisable by ff:fe in the middle of the last 64 bits. Modern systems use privacy addresses (RFC 8981) or stable random identifiers (RFC 7217) instead.
What is the reverse DNS zone for my IPv6 prefix?
Each hex digit becomes a label in reverse order under ip6.arpa, so 2001:db8::/32 becomes 8.b.d.0.1.0.0.2.ip6.arpa. Prefixes that aren't multiples of 4 bits are delegated as several zones.

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