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/{{ currentPrefix }} {{ ptrMarkerLabel }} {{ routeModeLabel }}
For example, 192.0.2.128/28 or 10.20.30.0/24.
Use a DNS name such as corp.example; a final dot is optional.
Whole seconds from 0 through 2,147,483,647.
s
Use an authoritative hostname such as ns1.corp.example.
Enter hostmaster@corp.example or an existing SOA RNAME.
YYYYMMDDnn is easy to operate, but any increasing unsigned 32-bit value is accepted.
Enter one hostname per line; two or more are recommended for delegated zones.
Example: 192.0.2.130,mail.corp.example.,3600,mail gateway
Rows stay in this browser and regenerate the handoff immediately.
Hyphen avoids slash handling surprises; this setting has no effect on octet-boundary zones.
How often secondary servers check for a newer serial.
s
How soon a secondary retries after a failed refresh.
s
How long a secondary serves the zone without a successful refresh.
s
The negative-cache TTL under current SOA interpretation.
s
Controls the RFC 2317 parent stubs; ignored for direct reverse zones.
Used only for a row with no hostname. Tokens: {last}, {offset}, {ip}, and {domain}.
Turn this option on when sort ptr records is required.
{{ sort_records ? 'On' : 'Off' }}
Turn this option on when generated comments is required.
{{ include_comments ? 'On' : 'Off' }} 
{{ computation.values.reverse_zone_text }}

{{ computation.values.parent_delegation_text }}
IPv4 Owner PTR target TTL Source Copy
{{ row.ip }} {{ row.owner }} {{ row.target }} {{ row.ttl }} {{ row.source }}
No valid PTR rows are present. —
Severity Check Current Action Copy
{{ row.severity }} {{ row.check }} {{ row.current }} {{ row.action }}
Reverse DNS (PTR) Checker Check PTR records for an IP or hostname, verify forward-confirmed reverse DNS, and compare expected names or public resolver views.
DNS Zone File Generator Draft a BIND or provider-ready DNS zone file with normalized records, SOA and TTL checks, plus mail and DNSSEC review warnings.
Nameserver Health Check Check a domain’s resolver-visible nameserver set and verify address coverage, SOA presence, and cross-resolver drift before a DNS cutover.
EDNS Client Subnet (ECS) Tester Compare DNS answers with and without an EDNS Client Subnet hint, then inspect answer steering, echoed scope, TTL drift, and privacy clues.

Reverse DNS answers an address-to-name question. An IPv4 address is reversed beneath in-addr.arpa, and a PTR record at that owner name points to a hostname. Mail systems, logs, monitoring platforms, and network operators use the result as an identity clue, but a PTR record does not prove that the hostname points back to the same address.

The organization that controls the address space normally controls its reverse DNS. For public addresses, that may be an internet service provider, hosting company, or regional registry delegate rather than the organization that controls the forward domain. A correct local zone file cannot replace the parent delegation needed to make the zone visible.

IPv4 reverse zones align naturally on octet boundaries because the labels are reversed octets. A /24 maps cleanly to a zone such as 2.0.192.in-addr.arpa.. A smaller block inside that /24, such as a /28, cannot be delegated through ordinary label boundaries. RFC 2317 solves this by creating a child zone and placing CNAME records in the parent /24 zone.

IPv4 block Usual reverse-zone treatment Important dependency
/8, /16, or /24 Direct octet-boundary zone Parent NS delegation to the exact reverse origin
/25 to /32 RFC 2317 child zone Parent NS records and per-address CNAME aliases
/9 to /23 off an octet boundary Parent-zone fragment in the nearest enclosing reverse zone Coordination with the operator of that enclosing zone

Every authoritative zone also needs an SOA record. Its serial tells secondary servers which copy is newer; refresh, retry, and expire values control transfer timing; and the minimum field participates in negative-cache behavior under modern DNS rules. These values are operational policy, not decoration. A serial that never increases can leave secondary servers on old data.

PTR targets should be absolute DNS names and usually correspond to stable forward records. Some systems expect forward-confirmed reverse DNS, where the PTR hostname resolves back to the original address. That relationship must be checked separately after the reverse zone is loaded and delegated.

How to Use This Tool:

Prepare the delegated IPv4 block, the authoritative server names, and the intended address-to-hostname mappings before generating zone text.

  1. Enter the IPv4 subnet and the forward hostname suffix. If the address is not the network base, the result normalizes it to the actual CIDR boundary.
  2. Set the default TTL, primary nameserver, responsible mailbox, increasing SOA serial, authoritative nameservers, and SOA timers.
  3. Add one PTR entry per address using a full IPv4 address or final octet, followed by an optional target, TTL, and note. Missing targets use the fallback hostname pattern.
  4. For blocks longer than /24, choose the RFC 2317 child-label style and decide whether parent CNAME coverage follows entered PTRs, usable host addresses, or every address.
  5. Review Reverse zone, Parent delegation, and Zone checks. Load both artifacts in the correct authoritative zones and verify the published PTR and SOA answers.

Interpreting Results:

Strategy identifies whether the block produces a direct octet-boundary zone, an RFC 2317 child zone, or a parent-zone fragment. When Parent required is true, the child zone alone is incomplete; resolvers also need the matching parent NS and CNAME records.

  • A normalization note means an address, mailbox, or hostname was converted to canonical zone-file form. Confirm the normalized value before publishing.
  • A warning about one nameserver, timer ordering, duplicate PTR rows, or a nonstandard serial pattern does not block generation, but it still needs an operator decision.
  • PTR count measures generated rows, not live DNS reachability. Query every authoritative server after loading the zone.

Technical Details:

IPv4 reverse owner names are built by reversing the address octets needed beneath the selected zone origin. The CIDR prefix determines how many octets belong in the origin and whether the remaining address space can be delegated directly.

Rule Core:

Condition Zone origin rule Parent artifact
Prefix is /8, /16, or /24 Reverse 1, 2, or 3 network octets beneath in-addr.arpa. No RFC 2317 CNAME set
Prefix is /25 to /32 Create a child label from the starting final octet and prefix, then append the parent /24 origin Child NS records plus CNAME aliases in the parent /24
Prefix is /9 to /23 and not /16 Use the nearest enclosing octet-boundary origin Generate a fragment for that parent zone and warn that it is not an independent classless delegation

Transformation Core:

Each PTR row passes through address resolution, subnet membership, target normalization, duplicate handling, and owner-name construction.

  1. A final octet is combined with the subnet's first three octets; a full address is used directly.
  2. The address must fall between the normalized network and broadcast addresses, inclusive.
  3. A missing hostname is filled from the pattern tokens {last}, {offset}, {ip}, and {domain}.
  4. A relative target is completed with the forward suffix; an absolute target keeps its own dotted name and receives a final dot.
  5. Duplicate addresses keep the first row, keep the last row, or retain all rows according to the selected policy. Optional sorting then orders rows by numeric address and target.

For an RFC 2317 child, parent CNAME coverage can include only addresses with PTR rows, all usable addresses, or the whole CIDR range. The usable mode excludes network and broadcast addresses except for /31 and /32 blocks.

Validation Boundaries:

Value Accepted boundary Additional rule
IPv4 prefix /8 through /32 Host bits are cleared to the network base
TTL and SOA timers 0 to 2,147,483,647 seconds Retry at or above refresh and expire at or below refresh produce warnings
SOA serial 0 to 4,294,967,295 Digits are required; values outside the ten-digit YYYYMMDDnn pattern produce a warning
PTR TTL 0 to 2,147,483,647 seconds An omitted row TTL inherits the zone default

Accuracy and Privacy Notes:

Zone generation happens in the browser and performs no live DNS lookup. It cannot confirm address ownership, parent delegation, zone loading, secondary transfers, forward-confirmed reverse DNS, or the policies of an email or hosting provider.

  • Validate the master-file syntax with the authoritative server software before reload.
  • Publish RFC 2317 child and parent records as one coordinated change.
  • Query each authoritative nameserver directly and compare SOA serials after deployment.

Worked Examples:

A /28 reverse delegation

For 192.0.2.128/28 with the hyphen style, the child origin is 128-28.2.0.192.in-addr.arpa. and the parent is 2.0.192.in-addr.arpa.. A PTR row for 192.0.2.130 becomes owner 130 in the child. With PTR-only parent coverage, the parent artifact adds a CNAME from 130 to 130.128-28.2.0.192.in-addr.arpa..

References: