PTR record generator: what reverse-DNS name does this IP need?
How does this check work, and what does the result tell you?
AdminKit's PTR record generator takes the IPv4 or IPv6 address, CIDR or in-addr.arpa/ip6.arpa name you paste, entirely in your browser, and computes the exact reverse-DNS query name and a sample PTR record line for it — it does no DNS lookup, it only computes the name you would query or create.
Part of the DNS cluster — more tools, guides and terms on dns.
Computed entirely in your browser — nothing you type is sent to AdminKit or anywhere else, and this tool does no DNS lookup. It only computes the name you would query or create.
What the result means
The reverse-DNS query name is the exact zone name you'd ask a DNS provider to publish a PTR record under, or query once one exists. Decoding an existing arpa name back to an IP confirms what address a name you were given actually corresponds to.
Next step
If a PTR record already exists at this name, confirm it with AdminKit's reverse DNS (PTR) lookup. If it doesn't exist yet, ask whoever controls the IP block's reverse zone — your ISP or hosting provider — to create it at this name.
Keep this result
Copy a link to this check so you can share it or run it again later. Want a heads-up if something changes? That's early access, not a live feature yet — tell us and we'll set it up by hand.
How it works and limits
Paste an IPv4 address, an IPv6 address, a CIDR, or an existing in-addr.arpa/ip6.arpa name below, and this tool
computes the reverse-DNS query name — or, run the other way, the IP address an existing arpa name was built from —
entirely in your browser. It does no DNS lookup at all: it only computes the name you would need to query or ask
your provider to create, the same way AdminKit’s reverse DNS (PTR) lookup tool queries a
record that already exists.
Why does an admin need to compute this name instead of just looking one up?
Because the name has to exist before a lookup can find anything. When you’re requesting a new PTR record from a
hosting provider, writing a reverse zone file by hand, or just verifying that a value your provider’s control
panel shows you is the right one, you need the exact in-addr.arpa or ip6.arpa name for your IP — not a live
query against a record that may not be published yet. This tool is the naming/zone half of that workflow; once a
record exists, confirm it resolved correctly with reverse DNS (PTR) lookup.
How the name is built
- IPv4 (RFC 1035 §3.5): the four dotted octets are
reversed and
.in-addr.arpais appended —192.0.2.5becomes5.2.0.192.in-addr.arpa. - IPv6 (RFC 3596 §2.5): the address is expanded to its
full 32 hex nibbles, each nibble is reversed individually, and
.ip6.arpais appended —2001:db8::1becomes1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa. RFC 8501 covers why IPv6 reverse DNS is often left unmanaged by ISPs in practice, even though the name itself is always computable this way. - A CIDR (e.g.
192.0.2.5/24): the/prefixis accepted and ignored — the name is always computed for the address itself, not the network’s base address. - An existing arpa name: paste it in and the tool decodes it back to the IPv4 or IPv6 address it was built from, which is useful for checking that a name you were given (or found in a zone file) actually corresponds to the IP you expect.
Limits
- This tool only computes a name. It never queries DNS, so it cannot tell you whether a PTR record for that name actually exists — use AdminKit’s reverse DNS (PTR) lookup for that.
- The hostname in the sample PTR record line is a placeholder you set yourself; this tool has no way to know what hostname a PTR record for your IP should actually point to.
- Computing the name does not mean you can publish it. Only whoever controls the IP block’s reverse zone — your ISP or hosting provider, via their registry delegation — can create a working PTR record at that name; see AdminKit’s subnet calculator if you need the network boundaries for the block first.
- An IPv6 address shown back after decoding an
ip6.arpaname is normalized to its compressed canonical form (RFC 5952), which may look different from — but is equivalent to — however the original address was written.
Reference: PTR record. For the live query against a record that already exists, use reverse DNS (PTR) lookup; for the general forward/reverse DNS lookup tool, see DNS lookup.
Frequently asked questions
How is this different from AdminKit's reverse DNS (PTR) lookup tool?
The reverse DNS (PTR) lookup tool queries DNS live to show the PTR record a given IP already resolves to. This PTR record generator does no lookup at all — it only computes the reverse-DNS zone name (in-addr.arpa or ip6.arpa) you would need to query or create for a given IP, which is what you need before a record exists or when you're building one by hand.
Why does IPv4 use in-addr.arpa but IPv6 use ip6.arpa?
They were defined at different times for different address sizes. RFC 1035 §3.5 defines in-addr.arpa for IPv4's 32-bit addresses, reversing the four dotted octets. RFC 3596 §2.5 defines ip6.arpa for IPv6's 128-bit addresses, reversing all 32 hex nibbles individually rather than four octets, since IPv6 has no equivalent dotted-octet grouping in its reverse zone.
Why are the octets or nibbles reversed in a reverse-DNS name?
DNS always delegates zones from the most general label on the right to the most specific label on the left, the same way a forward name like www.example.com delegates from .com inward. A reverse zone mirrors that: 192.0.2.0/24's administrator is delegated the zone 2.0.192.in-addr.arpa, so reversing the address puts the network portion (the part the registry delegates) on the right and the host portion on the left, exactly like a forward name.
Can I just create a PTR record with the name this tool shows me?
Only if whoever controls the IP block has delegated that reverse zone to your DNS provider — most individual users and even most hosting customers cannot publish an arbitrary PTR record themselves. This tool computes the name correctly regardless, but publishing it (or getting it published through your provider's support) is a separate step this tool does not perform.