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..
Copyright 2015 Rackspace Hosting
Licensed under the Apache License, Version 2.0 (the "License"); you may
not use this file except in compliance with the License. You may obtain
a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
License for the specific language governing permissions and limitations
under the License.
==========================
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,
.. code-block:: bash
$ 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
.. code-block:: bash
$ 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.
1. A domain that should be pointed to from the IP
2. 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.
.. code-block:: http
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.
.. code-block:: http
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.
.. code-block:: http
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.
.. code-block:: http
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.
.. code-block:: http
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.
.. code-block:: http
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!
.. code-block:: bash
$ 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.
.. code-block:: http
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.
.. code-block:: http
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.`
.. code-block:: bash
$ 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.
.. _RFC 2317: https://tools.ietf.org/html/rfc2317
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