Why you need Reverse DNS
Posted by Miles Evans
Standard DNS is a well known concept. You create a record with your domain registrar pointing your domain name to an IP address (ie: your web server). Your DNS server then propagates this record to DNS servers around the world and voila, you are directing traffic.
Reverse DNS is a bit different and in this article I will explain why not implementing it is costing you money.
First of all Reverse DNS or rDNS works in the opposite manner to standard DNS in that it takes an IP address and resolves this to your domain name. Reverse DNS lookups started to be deployed a couple of years back as a way to combat spam for large ISP’s. Mail spammers often use an IP address that does not correctly resolve to their host name. AOL, Yahoo, Verizon, and many others will not receive email from a server that fails a Reverse DNS lookup. You likely see these failed mail attempts in your inbox.
Hopefully you see why this is important now. Based on figures from a large forum that requires email verification to join, we were losing around 15% of our signups. Reverse DNS might be the most overlooked yet essential server setting I know of.
Alright so how do you get reverse DNS working for your own production machines? The short answer is to contact your ISP and either:
- Tell them to add a reverse DNS record for your domain to their DNS server.
- Tell them to delegate authority for your reverse DNS to your own DNS servers (provided you know how to do this).
Or:
In most cases your ISP will be familiar with these types of requests and method 1 will be sufficient. For more information on how to correctly configure DNS for reverse lookups you. or your ISP, can check out RFC 1912 Section 2.1 or this quick DNS primer.
Posted Jul 02, 2006 at 05:22 AM | Permalink | Trackback URL | Del.icio.us | DIGG!
