IPv6 Reverse DNS (rdns6)¶

The IPv6 reverse-DNS tool is in the Tool Drawer on the IPv6 tab. Enter an IPv6 address with an optional nibble-aligned prefix length, and the tool returns the corresponding ip6.arpa zone-delegation name per RFC 3596.

This is the IPv6 counterpart to the IPv4 Reverse DNS Zones tool, focused on producing a clean, copy-pasteable zone name. Use the IPv4 rdns tool for full BIND zone-file generation; the IPv6 reverse-DNS tool is deliberately scoped to the zone name itself.

Synopsis¶

Input	Required	Type	Notes
Address	Yes	string	Any valid IPv6 literal (compressed/expanded)
Prefix	No	integer	0..128, must be a multiple of 4

Output	Type	Notes
address	string	Echoed input address
prefix	integer	Echoed prefix (defaults to 128 when omitted)
arpa	string	The `ip6.arpa` zone-delegation name (RFC 3596)

What is `ip6.arpa`?¶

The ip6.arpa namespace is the IPv6 reverse-DNS tree. Every IPv6 address maps to a unique PTR record under ip6.arpa formed by reversing the 32 nibbles of the address and joining them with dots.

For zone delegation, you publish a name covering the most-significant N nibbles (where N = prefix / 4), reversed. RFC 3596 requires N to land on a nibble boundary — a multiple of 4 bits — because the DNS hierarchy splits one nibble per label.

Examples¶

Address	Prefix	`ip6.arpa` name
`2001:db8::1`	(none)	`1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa`
`2001:db8:abcd::`	48	`d.c.b.a.8.b.d.0.1.0.0.2.ip6.arpa`
`2001:db8::`	64	`0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa`
`fe80::1`	64	`0.0.0.0.0.0.0.0.0.0.0.0.0.8.e.f.ip6.arpa`
`2001:db8::`	0	`ip6.arpa`

Validation rules¶

Address must parse via inet_pton() to a 16-byte IPv6 literal. Both compressed (2001:db8::1) and expanded (2001:0db8:0000:…) forms work and canonicalise to the same nibble sequence.
Prefix (if present) must be in the range 0..128 and must be a multiple of 4. Non-nibble-aligned values such as 49 or 65 are rejected with a clear error — RFC 3596 zone delegation has no defined representation off a nibble boundary.
A prefix of 0 returns the bare suffix ip6.arpa.

API¶

POST /api/v1/rdns6

{
  "address": "2001:db8::",
  "prefix": 64
}

Response:

{
  "ok": true,
  "data": {
    "address": "2001:db8::",
    "prefix": 64,
    "arpa": "0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa"
  }
}

The prefix field is optional — omit it (or pass 128) to get the full reverse name for a single host.

Errors¶

Error	Cause
`Invalid IPv6 address`	Address fails `inet_pton()`
`Prefix length must be 0..128`	Prefix outside the legal IPv6 prefix range
`Prefix length must be a multiple of 4 for ip6.arpa zone delegation`	Non-nibble-aligned prefix (e.g. `/49`, `/65`)

Shareable URLs¶

The tool supports the standard tab + tool URL pattern:

?tab=ipv6&rdns6_address=2001:db8::&rdns6_prefix=64

Open the link and the rdns6 drawer auto-opens with the result already calculated.