Reverse Zones

Reverse DNS maps IP addresses to names via zones named after the reversed IP. ScaiDNS has a dedicated API that accepts CIDR input and manages PTR records by IP instead of by reversed octets.

Base path: /api/v1/reverse-zones/ Required permission: domains:* and records:* on the reverse zone

Concepts#

An IPv4 reverse zone's name is derived from reversing the octets of the network and appending .in-addr.arpa:

192.0.2.0/24 → 2.0.192.in-addr.arpa
10.0.0.0/16 → 0.10.in-addr.arpa
10.0.0.0/8 → 10.in-addr.arpa

IPv6 reverse zones use the nibble form with .ip6.arpa.

ScaiDNS hides this by accepting CIDR input directly. You give it 192.0.2.0/24, it creates 2.0.192.in-addr.arpa and lets you add PTR records keyed by IP.

Preview#

Before creating, preview what zones will be created from a CIDR:

bash
curl -X POST https://scaidns.scailabs.ai/api/v1/reverse-zones/preview \
  -H "X-API-Key: $SCAIDNS_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"cidr": "10.0.0.0/16"}'

python
resp = httpx.post(
    "https://scaidns.scailabs.ai/api/v1/reverse-zones/preview",
    headers={"X-API-Key": os.environ["SCAIDNS_API_KEY"]},
    json={"cidr": "10.0.0.0/16"},
)
print(resp.json())

typescript
const resp = await fetch(
  "https://scaidns.scailabs.ai/api/v1/reverse-zones/preview",
  {
    method: "POST",
    headers: {
      "X-API-Key": process.env.SCAIDNS_API_KEY!,
      "Content-Type": "application/json",
    },
    body: JSON.stringify({ cidr: "10.0.0.0/16" }),
  },
);
console.log(await resp.json());

Response includes the zone name that would be created and the IP range it covers:

json
{
  "zone_name": "0.10.in-addr.arpa",
  "start_ip": "10.0.0.0",
  "end_ip": "10.0.255.255",
  "ip_count": 65536,
  "domain_type": "reverse_ipv4"
}

Create from CIDR#

bash
curl -X POST https://scaidns.scailabs.ai/api/v1/reverse-zones/ \
  -H "X-API-Key: $SCAIDNS_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "cidr": "192.0.2.0/24",
    "default_ttl": 3600,
    "description": "Office subnet"
  }'

Returns a domain record like any other — you'll get a pending_validation zone that you then validate through the same TXT mechanism as forward zones. See Domain Validation.

Reverse zones often skip validation in internal deployments; a user with the validation_bypass permission can create them ready-to-use.

Supported prefix lengths#

IPv4:

Prefix	Example	Zones created
`/8`	`10.0.0.0/8`	One zone: `10.in-addr.arpa`
`/16`	`10.0.0.0/16`	One zone: `0.10.in-addr.arpa`
`/24`	`192.0.2.0/24`	One zone: `2.0.192.in-addr.arpa`
`/25`–`/32`	`192.0.2.0/28`	Classless (RFC 2317) — creates a zone with a hyphenated name

IPv6:

Prefix	Zones created
`/4`, `/8`, ... `/124` (multiples of 4)	Single zone
Other	Not yet supported

For subnets that don't align to octet/nibble boundaries, RFC 2317 classless delegation is used automatically — the zone name includes the prefix length.

PTR records#

PTR records live inside reverse zones. ScaiDNS lets you address them by IP rather than by reversed name.

Create a PTR#

bash
curl -X POST https://scaidns.scailabs.ai/api/v1/reverse-zones/$ZONE_ID/ptr \
  -H "X-API-Key: $SCAIDNS_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "ip": "192.0.2.10",
    "hostname": "host-10.example.com.",
    "ttl": 3600
  }'

python
resp = httpx.post(
    f"https://scaidns.scailabs.ai/api/v1/reverse-zones/{ZONE_ID}/ptr",
    headers={"X-API-Key": os.environ["SCAIDNS_API_KEY"]},
    json={
        "ip": "192.0.2.10",
        "hostname": "host-10.example.com.",
        "ttl": 3600,
    },
)

typescript
await fetch(
  `https://scaidns.scailabs.ai/api/v1/reverse-zones/${zoneId}/ptr`,
  {
    method: "POST",
    headers: {
      "X-API-Key": process.env.SCAIDNS_API_KEY!,
      "Content-Type": "application/json",
    },
    body: JSON.stringify({
      ip: "192.0.2.10",
      hostname: "host-10.example.com.",
      ttl: 3600,
    }),
  },
);

ScaiDNS validates that the IP falls within the zone's CIDR, then creates the underlying PTR record.

List PTR records#

bash
curl https://scaidns.scailabs.ai/api/v1/reverse-zones/$ZONE_ID/ptr \
  -H "X-API-Key: $SCAIDNS_API_KEY"

Returns a list with ip, hostname, ttl, and the underlying record ID.

Delete a PTR#

bash
curl -X DELETE "https://scaidns.scailabs.ai/api/v1/reverse-zones/$ZONE_ID/ptr/192.0.2.10" \
  -H "X-API-Key: $SCAIDNS_API_KEY"

Delete by IP address directly — no need to look up the record ID.

Bulk create#

bash
curl -X POST https://scaidns.scailabs.ai/api/v1/reverse-zones/$ZONE_ID/ptr/bulk \
  -H "X-API-Key: $SCAIDNS_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "records": [
      {"ip": "192.0.2.10", "hostname": "host-10.example.com."},
      {"ip": "192.0.2.11", "hostname": "host-11.example.com."},
      {"ip": "192.0.2.12", "hostname": "host-12.example.com."}
    ]
  }'

Global reverse lookup#

Given only an IP, find the PTR and owning zone across all of your tenant's reverse zones:

bash
curl https://scaidns.scailabs.ai/api/v1/reverse-zones/lookup/192.0.2.10 \
  -H "X-API-Key: $SCAIDNS_API_KEY"

Response:

json
{
  "ip": "192.0.2.10",
  "hostname": "host-10.example.com.",
  "zone_id": "z_abc123",
  "zone_name": "2.0.192.in-addr.arpa"
}

Advanced records on reverse zones#

Reverse zones occasionally need records other than PTR — notably the zone's own NS and SOA records are managed automatically, but you may want to add extra NS (for delegation) or TXT (for documentation).

Use the standard /api/v1/domains/{domain_id}/records endpoint on the reverse zone's domain ID. The reverse zone API is a convenience layer for PTR records; the full record API works just fine.

What's next#

Managing Records — generic record management (also works on reverse zones).
Reverse Zones reference — endpoint details.