IPv6 Expand, Compress and Subnet Tool
Expand or compress an IPv6 address to RFC 5952 form, see its type and prefix range, count its addresses and get the ip6.arpa reverse DNS name.
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Input
Expand, compress and inspect IPv6 addresses
Output
2001:db8::ff00:42:8329
| Compressed | 2001:db8::ff00:42:8329 |
|---|---|
| Expanded | 2001:0db8:0000:0000:0000:ff00:0042:8329 |
| Type | Documentation (RFC 3849) |
| Network | 2001:db8::/64 |
| Last address | 2001:db8::ffff:ffff:ffff:ffff |
| Addresses in prefix | 2^64 |
| Reverse DNS (PTR) | 9.2.3.8.2.4.0.0.0.0.f.f.0.0.0.0.0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa |
The compressed form follows RFC 5952: lowercase, leading zeros dropped and the longest run of zero groups written as ::. Use it in logs and configs so the same address is always the same string. A /64 is the standard size of one LAN.
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About this tool
Method, assumptions, practical next steps, and limits.
One address, one string
IPv6 allows many spellings of the same address. RFC 5952 picks one: lowercase, no leading zeros, and the longest run of two or more zero groups replaced by ::. Logs, allow-lists and database keys should store that form, or the same client appears as several addresses.
Sizes
A single LAN is a /64, so stateless address autoconfiguration has 64 bits to work with. Providers typically delegate a /48 or /56 to a site. Rate limits and blocklists keyed on single IPv6 addresses are easy to evade, because one client controls a whole /64; key them on the /64 instead.