What this toolkit does
Give it any IPv6 address and it rewrites that address every way you might need it. It expands the address to its full eight-group form, compresses it to the canonical short form, builds the ip6.arpa reverse-DNS name for PTR records, and classifies which special-purpose block (if any) the address belongs to. All of that maths happens locally in your browser — the address you paste is never transmitted — so it's safe to run on internal, link-local, or otherwise sensitive addresses.
Why IPv6 has so many notations
IPv6 addresses are 128 bits — 32 hex digits. Writing them out fully is unwieldy, so RFC 4291 defines two compressions:
- Leading zero suppression. Each 16-bit group can drop leading zeros, so
2001:0db8:0000:0000:0000:0000:0000:0001becomes2001:db8:0:0:0:0:0:1. - The double-colon (
::) substitution. Exactly one run of consecutive zero groups can be replaced with two colons.2001:db8:0:0:0:0:0:1→2001:db8::1.
The "canonical" form (RFC 5952) tightens this further: use lowercase, drop leading zeros, apply :: to the longest zero run (and the first such run if there are ties).
Reverse DNS in IPv6
PTR records for IPv6 live under the ip6.arpa tree. Each nibble (half-byte) becomes a label, in reverse order. So 2001:db8::1 reverses to 1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa. You can query that PTR with the DNS tool.
Special ranges to know
| Range | Name | Use |
|---|---|---|
::/128 | Unspecified | "No address" placeholder |
::1/128 | Loopback | Equivalent to IPv4 127.0.0.1 |
fe80::/10 | Link-local | Auto-configured per interface; never routed |
fc00::/7 | Unique local (ULA) | Private networks (IPv4 RFC 1918 equivalent) |
2000::/3 | Global unicast | The routable internet |
2001:db8::/32 | Documentation | Examples only — never routed |
ff00::/8 | Multicast | One-to-many, scoped (link / site / org / global) |
Reading the prefix length
Most of the ranges above are written with a slash and a number, such as fe80::/10. That number is the prefix length — how many leading bits are fixed and define the network, leaving the rest for hosts. A typical site is delegated a /48, splits it into /64 subnets, and runs every LAN as a single /64 because that is what Stateless Address Autoconfiguration (SLAAC) assumes. If you need to slice or aggregate prefixes, the CIDR calculator handles the bit arithmetic for both IPv4 and IPv6.
Frequently asked questions
What is the difference between expanded and compressed notation?
Both describe the same 128-bit value. The expanded form spells out all eight groups with full leading zeros, which is unambiguous and easy to parse by hand. The compressed form drops leading zeros and collapses the longest run of zero groups into :: — shorter, and the canonical form RFC 5952 expects in configuration files and logs.
Why can the double colon appear only once?
The :: stands in for an unknown number of all-zero groups. If it appeared twice, nothing would tell a parser how many zero groups belong to each gap, so the address would be ambiguous. Using it once means the surrounding groups pin down exactly how many zeros it represents.
Does anything I type get sent to a server?
No. Every operation here runs in your browser, so the address you enter never leaves the page — safe for internal or sensitive addresses.
Related tools
Check whether your own connection actually has v6 with the IPv6 connectivity test, convert between address families using IPv4 to IPv6, query the reverse record you generate here with the DNS lookup, and brush up on terminology in the networking glossary.