When you enter a domain name into your browser, the DNS system will find the IP address of the server the domain is associated with.
A reverse DNS lookup does the opposite. It establishes what domain is associated with the IP address. This is a useful setting to configure for anyone but essential for those running a mail server for example.
As mentioned, it is an essential setting for those running a mail server as many recipient servers will reject, or mark as spam, all email that originates from an 'unauthenticated' server.
This basically means that once the sending IP address has been checked, if the Reverse DNS does not match the sending domain, then it is classed as 'unauthenticated'.
I put 'unauthenticated' in quotes as it is does not guarantee acceptance of email or anything like that. It's just that non-matching or generic RDNS settings are often rejected out of hand.
It can also be very useful (and was the original driving force of RDNS) when tracking down network issues. When 'pinging' a website or IP address, one part of the output is the server's RDNS record.
Let's go ahead and set it for our Slice.
As you would imagine, we need to log into the SliceManager at https://manage.slicehost.com.
Once logged in, click the DNS tab were you will be faced with this:
Next click the 'Reverse DNS' link.
You will see a simple page with a generic RDNS already set:
That may be fine for some, but let's go ahead and customise it.
In this example, I will set the RDNS to 'mail.mynewdomain.com' which would coincide with my mail server:
Once saved, you can check the entry or, indeed, change it whenever you want to:
Setting an RDNS is essential for anyone running a mail server and desirable for the rest of us.
Luckily, the SliceManager makes this configuration nice and easy.