DNS PTR record when domain on shared IP address

Question

I own a typical shared IP hosting plan and domain. I can modify the DNS of the domain from the control panel. The mailserver shares the same IP address, so my typical DNS config is:

www.mydomain.com   A      -> myIP
mydomain.com       A      -> myIP
ftp.mydomain.com   A      -> myIP
mail.mydomain.com  A      -> myIP
mydomain.com       MX(10) -> myIP

I read some Q&A on this site where they suggest to add PTR record mainly for mailserver.

I would like to add PTR record to my domain, I have got two questions:

1) can PTR record be added even if the hosting/mailserver are on a shared IP address? Or do I need a dedicated IP.

2) How do I setup PTR record, I mean does it look like A record:

mydomain.com (PTR) -> myIP

Solution 1

You can't create a PTR record for the ip address in your domain name DNS zone. The PTR record needs to be created in the rDNS zone by the owner of the netblock that encompasses your ip address. You'll need to speak to whomever you get the ip address from and ask them to create a PTR record for you.

Solution 2

You can only set up a PTR record if you are the delegated maintainer of the relevant portion of the in-addr.arpa. domain name.

In your case that would be your web host. If you have a dedicated IP address then they should allow you to request the appropriate entry. On the other hand, if you have a shared IP address then it's very unlikely that they would permit this.

For what it's worth, if your mail server is called mail.example.com and its IP address is w.x.y.z then the appropriate DNS record would look like:

z.y.x.w.in-addr.arpa. IN PTR mail.example.com.

Comments

[Marco Demaio]

Thnaks, I know how to use the control panel but could someone expalin what record do I need to add in order to place a PTR record. Let's simply say I have the domain "mydomain.com" that point to IP "myip"

[TomTom]

I dont know because I don'T even know what control panel. I suggest you just contact your hoster support. They will be able to help you out.

[Marco Demaio]

Hmmm, so what happens if I add in the DNS record of mydomain.com: "myip.in-addr.arpa IN PTR mail.mydomain.com" actually the DNS control panel let me do this, but is then useless?

[Marco Demaio]

So why mydomain.com DNS control panel lets me add PTR records?

[Alnitak]

you can't do that - it's illegal. Note the trailing '.' on 'in-addr.arpa.'. That's a full qualified domain name, in a separate zone, so you can't possibly add it to 'myexample.com'.