How To Manage PTR Records¶

PTR Record Basics¶

PTR records provide a reverse mapping from a single IP or set of IP addresses to a domain. For example,

$ dig -x 192.0.2.12 +short
example.org.

The way this works in the DNS system is through the in-addr.arpa. zone. For example

$ dig example.org +short
192.0.2.12
$ dig -x 192.0.2.12
; <<>> DiG 9.9.5-3ubuntu0.1-Ubuntu <<>> -x 192.0.2.12
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 3431
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4000
;; QUESTION SECTION:
;12.2.0.192.in-addr.arpa.   IN      PTR      example.org.

;; AUTHORITY SECTION:
12.2.0.192.in-addr.arpa. 3600 IN     NS      ns1.example.org.

;; Query time: 40 msec
;; SERVER: 127.0.0.1#53(127.0.0.1)
;; WHEN: Fri Feb 20 19:05:44 UTC 2015
;; MSG SIZE  rcvd: 119

In the question section we see the address being requested from the DNS system as 12.2.0.192.in-addr.arpa.. As you can see, the IP address has been reversed in order to function similarly to a domain name where the more specific elements come first. The reversed IP address is then added to the in-addr.arpa. domain, at which point the DNS system can perform a simple look up to find any PTR records that describe what domain name, if any, maps to that IP.

Create a PTR Record in Designate¶

To create a PTR record in Designate, there are two requirements.

A domain that should be pointed to from the IP

A in-addr.arpa. zone entry that will receive the actual PTR record

Using the V2 API¶

To begin let’s create a zone that we want to return when we do our reverse lookup.

POST /v2/zones HTTP/1.1
Accept: application/json
Content-Type: application/json

{
  "name": "example.org.",
  "email": "admin@example.org",
  "ttl": 3600,
  "description": "A great example zone"
}

Here is the JSON response describing the new zone.

HTTP/1.1 202 Accepted
Location: http://127.0.0.1:9001/v2/zones/fe078042-0aa3-4500-a81e-8f328f79bf75
Content-Length: 476
Content-Type: application/json; charset=UTF-8
X-Openstack-Request-Id: req-bfcd0723-624c-4ec2-bbd5-99e985efe8db
Date: Fri, 20 Feb 2015 21:20:28 GMT
Connection: keep-alive

{
  "email": "admin@example.org",
  "project_id": "noauth-project",
  "action": "CREATE",
  "version": 1,
  "pool_id": "794ccc2c-d751-44fe-b57f-8894c9f5c842",
  "created_at": "2015-02-20T21:20:28.000000",
  "name": "example.org.",
  "id": "fe078042-0aa3-4500-a81e-8f328f79bf75",
  "serial": 1424467228,
  "ttl": 3600,
  "updated_at": null,
  "links": {
    "self": "http://127.0.0.1:9001/v2/zones/fe078042-0aa3-4500-a81e-8f328f79bf75"
  },
  "description": "A great example zone",
  "status": "PENDING"
}

Note

The status is PENDING. If we make a GET request to the self field in the zone, it will most likely have been processed and updated to ACTIVE.

Now that we have a zone we’d like to use for our reverse DNS lookup, we need to add an in-addr.arpa. zone that includes the IP address we’ll be looking up.

Let’s configure 192.0.2.11 to return our example.org. domain name when we do a reverse look up.

POST /v2/zones HTTP/1.1
Accept: application/json
Content-Type: application/json

{
  "name": "11.2.0.192.in-addr.arpa.",
  "email": "admin@example.org",
  "ttl": 3600,
  "description": "A in-addr.arpa. zone for reverse lookups."
}

As you can see, in the name field we’ve reversed our IP address and used that as a subdomain in the in-addr.arpa. zone.

Here is the response.

HTTP/1.1 202 Accepted
Location: http://127.0.0.1:9001/v2/zones/1bed5d24-d487-4410-b813-f1c637db0ba3
Content-Length: 512
Content-Type: application/json; charset=UTF-8
X-Openstack-Request-Id: req-4e691123-045e-4f8e-ae50-b5eabb5af3fa
Date: Fri, 20 Feb 2015 21:35:41 GMT
Connection: keep-alive

{
  "email": "admin@example.org",
  "project_id": "noauth-project",
  "action": "CREATE",
  "version": 1,
  "pool_id": "794ccc2c-d751-44fe-b57f-8894c9f5c842",
  "created_at": "2015-02-20T21:35:41.000000",
  "name": "11.2.0.192.in-addr.arpa.",
  "id": "1bed5d24-d487-4410-b813-f1c637db0ba3",
  "serial": 1424468141,
  "ttl": 3600,
  "updated_at": null,
  "links": {
    "self": "http://127.0.0.1:9001/v2/zones/1bed5d24-d487-4410-b813-f1c637db0ba3"
  },
  "description": "A in-addr.arpa. zone for reverse lookups.",
  "status": "PENDING"
}

Now that we have our in-addr.arpa. zone, we add a new PTR record to the zone.

POST /v2/zones/1bed5d24-d487-4410-b813-f1c637db0ba3/recordsets HTTP/1.1
Content-Type: application/json
Accept: application/json

{
  "name": "11.2.0.192.in-addr.arpa.",
  "description": "A PTR recordset",
  "type": "PTR",
  "ttl": 3600,
  "records": [
    "example.org."
  ]
}

Here is the response.

HTTP/1.1 202 Accepted
Location: http://127.0.0.1:9001/v2/zones/1bed5d24-d487-4410-b813-f1c637db0ba3/recordsets/a3dca24e-3eba-4523-8607-c0ad4b9a9272
Content-Length: 499
Content-Type: application/json; charset=UTF-8
X-Openstack-Request-Id: req-5b7044d0-591a-445a-839f-1403b1455824
Date: Fri, 20 Feb 2015 21:42:45 GMT
Connection: keep-alive

{
  "type": "PTR",
  "action": "CREATE",
  "version": 1,
  "created_at": "2015-02-20T21:42:45.000000",
  "zone_id": "1bed5d24-d487-4410-b813-f1c637db0ba3",
  "name": "11.2.0.192.in-addr.arpa.",
  "id": "a3dca24e-3eba-4523-8607-c0ad4b9a9272",
  "ttl": 3600,
  "records": [
    "example.org."
  ],
  "updated_at": null,
  "links": {
    "self": "http://127.0.0.1:9001/v2/zones/1bed5d24-d487-4410-b813-f1c637db0ba3/recordsets/a3dca24e-3eba-4523-8607-c0ad4b9a9272"
  },
  "description": "A PTR recordset",
  "status": "PENDING"
}

We should now have a correct PTR record assigned in our nameserver that we can test.

Note

As the in-addr.arpa. zone is considered an admin zone, you may need to get admin rights in order to create the necessary subdomains.

Let’s test it out!

$ dig @localhost -x 192.0.2.11

; <<>> DiG 9.9.5-3ubuntu0.1-Ubuntu <<>> @localhost -x 192.0.2.11
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 32832
;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 1, ADDITIONAL: 1
;; WARNING: recursion requested but not available

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;11.2.0.192.in-addr.arpa.    IN      PTR

;; ANSWER SECTION:
11.2.0.192.in-addr.arpa. 3600 IN     PTR     example.org.

;; AUTHORITY SECTION:
11.2.0.192.in-addr.arpa. 3600 IN     NS      ns1.example.org.

;; Query time: 3 msec
;; SERVER: 127.0.0.1#53(127.0.0.1)
;; WHEN: Fri Feb 20 21:45:53 UTC 2015
;; MSG SIZE  rcvd: 98

As you can see from the answer section everything worked as expected.

Advanced Usage¶

You can add many PTR records to a larger subnet by using a more broadly defined in-addr.arpa. zone. For example, if we wanted to ensure any IP in a subnet resolves to a specific domain.

POST /v2/zones HTTP/1.1
Accept: application/json
Content-Type: application/json

{
  "name": "2.0.192.in-addr.arpa.",
  "ttl": 3600,
  "email": "admin@example.com"
}

We then could use the corresponding domain to create a PTR record for a specific IP.

POST /v2/zones/$domain_uuid/recordsets HTTP/1.1
Accept: application/json
Content-Type: application/json

{
  "name": "3.2.0.192.in-addr.arpa.",
  "type": "PTR"
  "ttl": 3600,
  "records": [
    "cats.example.com."
  ]
}

When we do our reverse look, we should see cats.example.com.

$ dig @localhost -x 192.0.2.3 +short
cats.example.com.

Success!

You can further specify in-addr.arpa. zones to chunks of IP addresses by using Classless in-addr.arpa. Delegation. See RFC 2317 for more information.

Note

In BIND9, when creating a new PTR we could skip the zone name. For example, if the zone is 2.0.192.in-addr.arpa., using 12 for the record name is ends up as 12.2.0.192.in-addr.arpa.. In Designate, the name of a record MUST be a complete host name.

How To Manage PTR Records

How To Manage PTR Records¶

PTR Record Basics¶

Create a PTR Record in Designate¶

Using the V2 API¶

Advanced Usage¶

designate 12.1.1.dev22

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