Diagnostics

Reverse PTR Zone

Paste an IP or a CIDR (IPv4 or IPv6 — auto-detected) and get the reverse name (in-addr.arpa / ip6.arpa) and a sample PTR zone block. Text manipulation only, no DNS queries.

redzilla.cl — ptr

Family IPv4

Zone 1.168.192.in-addr.arpa

$ORIGIN 1.168.192.in-addr.arpa.

PTR zone block

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How reverse DNS works

IPv4 The reverse name of a.b.c.d is d.c.b.a.in-addr.arpa (octets reversed). For a /24 the zone is c.b.a.in-addr.arpa and each host is a PTR record.

IPv6 The 32 nibbles are expanded, reversed and suffixed with .ip6.arpa. Each nibble (4 bits) is one label.

/24 /16 /8 Only prefixes aligned to an octet (IPv4) or to a nibble multiple of 4 (IPv6) have a "clean" reverse zone. For /16 and /8 we show the zone and a template, not thousands of lines.

RFC 2317 For IPv4 prefixes longer than /24 (e.g. /27) classless delegation is used (CNAME); here we generate the range's PTR records for reference.

Runs locally in your browser · no sign-up · nothing leaves your browser.

How it works

The tool takes an IP or CIDR (IPv4 or IPv6, auto-detected) and generates the matching reverse DNS name: for IPv4 it reverses the octets and appends in-addr.arpa (the reverse of 192.168.1.10 is 10.1.168.192.in-addr.arpa); for IPv6 it expands the 32 hexadecimal nibbles, reverses them and appends ip6.arpa. It also builds a ready-to-paste PTR zone block, with $ORIGIN and an editable hostname template using the {n}, {ip} and {last} variables.

Behavior depends on the prefix: a /24 generates the PTR records for every host (capped at 512 lines); /8 and /16 show the zone plus a template instead of thousands of records; IPv4 prefixes longer than /24 (such as /27) are generated inside the containing /24 zone, the classless delegation scenario of RFC 2317; and in IPv6 only prefixes that are multiples of 4 have a clean ip6.arpa zone, because delegations happen on nibble boundaries. Everything is pure text manipulation: no DNS query is ever made.

Example: reverse zone for 192.168.1.0/24

The three network octets are reversed: the zone is 1.168.192.in-addr.arpa and the $ORIGIN is 1.168.192.in-addr.arpa..
Each host uses its last octet as the relative name: 10 IN PTR host-11.example.com. corresponds to 192.168.1.10.
The tool generates all 256 records of the block, ready to copy into the zone file.

Frequently asked questions

What is a PTR record for and who needs it?

A PTR resolves an IP to a name (reverse DNS), the opposite of an A record. It is nearly mandatory for mail servers: many destinations reject or flag as spam any mail from IPs without a PTR consistent with the HELO. Logs, traceroute and diagnostic tools also use it to show names instead of IPs.

Who can create the PTR record for my public IP?

Only whoever administers the reverse delegation of the block, usually your ISP or cloud provider. You can generate the zone content with this tool, but if the IP belongs to your provider you must ask them to load the PTR or delegate the reverse zone to you.

What happens to the reverse zone if my block is a /27 instead of a /24?

in-addr.arpa zones are delegated on octet boundaries, so a /27 has no clean zone of its own. The standard solution is classless delegation per RFC 2317: the /24 owner creates CNAME records pointing to a subzone of yours. The tool generates the PTRs of the range inside the containing /24 zone as a reference.

Does the tool query DNS servers or expose my ranges?

No. It is pure text manipulation running entirely in your browser: no DNS query is made and the IP or CIDR is never sent to a server, so you can use it with internal ranges without exposing them.

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Disclaimer

We take great care to keep every tool accurate and review it thoroughly; even so, we can't guarantee it is free of errors or take responsibility for how the results are used. We recommend double-checking anything critical.

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