Type an IPv4 or IPv6 address (with an optional CIDR prefix) and get the reversed DNS name — 4.3.2.1.in-addr.arpa for v4, and the fully-expanded nibble.…ip6.arpa form for v6. Includes the zone origin, a starter BIND PTR record, and the RFC 2317 classless delegation form for /25–/31 v4 zones.
Drop this into the reverse zone that covers this address. The $ORIGIN line sets the zone tail so the PTR is written as the short host-part only.
IPv4. The address a.b.c.d reverses to d.c.b.a.in-addr.arpa. The octets flip because DNS is read most-specific first — the same way you'd read www.example.com right-to-left when carving up delegation. Each octet stays a decimal integer; no zero-padding.
IPv6. The 128-bit address is expanded to 32 hex nibbles, each nibble becomes its own label, and the order is fully reversed. 2001:db8::1 expands to 20010db8000000000000000000000001 and then reverses into 32 dotted labels ending in ip6.arpa. Uppercase is legal but the tool emits lowercase — matches RFC 3596 and every operator style guide.
CIDR / zone origin. The zone that carries the PTR is the reverse name of the network. A /24 (v4) trims one label off the address; a /16 trims two. IPv6 zones trim one nibble label per 4 bits of prefix — a /48 has 12 nibbles left, so 12 labels before ip6.arpa.
RFC 2317 classless delegation. ISPs sub-delegate ranges smaller than a /24 by using a dashed label: <first-host>-<prefix>.<C.B.A>.in-addr.arpa, then CNAME-ing every octet inside that range to the child zone. This tool emits the delegation zone name whenever your prefix is /25–/31.