Expand · compress · reverse

The IPv6 toolkit.

Expand or compress IPv6 notation, generate the ip6.arpa reverse-DNS name, and identify which special range an address falls in. All math is client-side; nothing leaves your browser.

Expanded (fully qualified)
2606:4700:4700:0000:0000:0000:0000:1111
Compressed (canonical)
2606:4700:4700::1111
Reverse DNS (ip6.arpa)
1.1.1.1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.7.4.0.0.7.4.6.0.6.2.ip6.arpa
Decimal
50543257694033307102031451402929180945
Hex
0x26064700470000000000000000001111
Global unicastRFC 3513

2000::/3 — the global routable IPv6 space.

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 2001:0db8:0000:0000:0000:0000:0000:0001 becomes 2001: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

RangeNameUse
::/128Unspecified"No address" placeholder
::1/128LoopbackEquivalent to IPv4 127.0.0.1
fe80::/10Link-localAuto-configured per interface; never routed
fc00::/7Unique local (ULA)Private networks (IPv4 RFC 1918 equivalent)
2000::/3Global unicastThe routable internet
2001:db8::/32DocumentationExamples only — never routed
ff00::/8MulticastOne-to-many, scoped (link / site / org / global)