Network · DNS
Reverse DNS PTR name generator.
Enter an IPv4 or IPv6 address to get its reverse lookup name (in-addr.arpa or ip6.arpa) and a BIND PTR record. Add a CIDR prefix to get the zone name to delegate, including RFC 2317 classless zones for blocks smaller than a /24.
Inputs
Result
Enter an address, then press Generate.
How the names are built
IPv4 (RFC 1035 section 3.5). Each octet becomes one label, in reverse order, under in-addr.arpa. The address 10.2.0.52 is looked up at 52.0.2.10.in-addr.arpa. Because the octets are reversed, a zone can be delegated at one, two or three octets: 10.in-addr.arpa for a /8, 168.192.in-addr.arpa for a /16, 1.168.192.in-addr.arpa for a /24.
IPv6 (RFC 3596 section 2.5). The address is written as 32 hexadecimal nibbles, the low-order nibble first, separated by dots, under ip6.arpa. The RFC's own example, 4321:0:1:2:3:4:567:89ab, becomes b.a.9.8.7.6.5.0.4.0.0.0.3.0.0.0.2.0.0.0.1.0.0.0.0.0.0.0.1.2.3.4.ip6.arpa. A zone is delegated on a nibble boundary, so a /32 is 8 nibbles and a /48 is 12.
Blocks smaller than a /24 (RFC 2317). A /24 zone can only be delegated once, so RFC 2317 adds a label made of the first address and the prefix length. 192.0.2.0/25 becomes the child zone 0/25.2.0.192.in-addr.arpa, and the parent /24 zone holds a CNAME such as 1 CNAME 1.0/25.2.0.192.in-addr.arpa. for each address. The RFC advises substituting a more conservative character, such as a hyphen, for the slash; this tool shows both. This page shows the naming convention only, not a full zone file.
Prefixes that do not end on a boundary. A /20 IPv4 block or a /34 IPv6 block is not one zone. It is delegated as several zones at the next octet or nibble boundary, and the tool lists them (up to 256 for IPv4, 16 for IPv6). This follows from the one-label-per-octet and one-label-per-nibble rules above rather than from a dedicated RFC section.
Specs: RFC 1035 (section 3.5, IN-ADDR.ARPA domain), RFC 3596 (section 2.5, IP6.ARPA domain) and RFC 2317 (classless IN-ADDR.ARPA delegation). Checked against the RFC text on 2026-09-30.
Frequently asked questions
Why is the address written backwards?
DNS names get more specific from right to left, while an IP address gets more specific from left to right. Reversing the octets lets a network owner hold the zone for exactly their own block, as RFC 1035 explains.
Do I need the trailing dot in a BIND file?
Yes when the name is fully qualified. Without it BIND appends the current zone origin. The generated records end in a dot for that reason.
Will this make my reverse lookup work?
No. The zone must also be delegated to your name servers by whoever holds the address block, usually your ISP or regional registry. This tool only builds the names.
Pure string arithmetic — no network access
Everything runs in your browser. The tool does not query DNS, and it does not check that an address is assigned, routed or delegated to you.