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Reverse DNS Zones

The calculator automatically displays the reverse DNS zone for each network.

IPv4

The Reverse DNS Zone row shows the in-addr.arpa zone that covers the subnet.

Prefix Zone
/24 1.168.192.in-addr.arpa
/16 168.192.in-addr.arpa
/8 192.in-addr.arpa
/25 0/25.1.168.192.in-addr.arpa (RFC 2317 classless delegation)

For non-octet-aligned prefixes (e.g. /25, /26) the calculator uses RFC 2317 CIDR notation.

IPv6

The Reverse DNS Zone row shows the ip6.arpa zone.

Prefix Zone
/32 8.b.d.0.1.0.0.2.ip6.arpa
/48 0.0.0.8.b.d.0.1.0.0.2.ip6.arpa

The zone is derived from the network address nibbles up to the prefix boundary.

REST API

The rdns field is included in all /api/v1/ipv4 and /api/v1/ipv6 responses. A dedicated /api/v1/rdns endpoint accepts a CIDR and returns a structured object:

{
  "ok": true,
  "data": {
    "zone": "1.168.192.in-addr.arpa",
    "format": "ipv4",
    "ttl": 3600,
    "record_count": 256,
    "content": "...<BIND zone file>..."
  }
}