Reverse DNS is one of those obscure things that you only seem to learn about when you become a pro at managing your website.
First you learn about web hosting and why it’s impossible to start a website without it, then you learn the importance of backing up your website so that all your hard work doesn’t vanish overnight, and then years later, when you’ve been successfully managing your website for a while, you somehow encounter the term “reverse DNS”, and a whole new world of possibilities opens up for you.
Well, today, we’re giving your internet knowledgebase a massive boost. We’re diving right into DNS.
Let’s begin, shall we?
Table of Contents
What is DNS?
Before we can get into reverse DNS, we have to wrap our minds around DNS.
DNS stands for Domain Name System, and it’s a list of every website’s domain name and corresponding IP address.
A website’s domain name will typically look like “www.websitenamehere.com”, but its computer-readable IP address will look more like “111.122.00.01”. The domain name is easier for you to remember than the IP address, but your computer needs to know a website’s IP address before it can load the website in your browser.
So, you can think of the DNS as a kind of phonebook, but for IP addresses. It lists websites by their domain name and shows their IP address.
(By the way, every server has an IP address. If you’re connected to the internet, your device has an IP address, even if you don’t have a website.)
What is a DNS lookup?
Let’s say that for some reason, you have a burning desire to visit www.websitenamehere.com. You type it into your browser, and your browser loads the page. But behind the scenes, your computer is performing a DNS lookup. (Since we’re going to compare it to a reverse DNS lookup, we can also call a DNS lookup by its more specific name: forward DNS lookup.)
What happens when you type a website into your browser is this: You enter the website into the browser, but your computer still needs to know the IP address before it can load the website. So, it forwards your domain name request to a DNS server that returns the corresponding IP address. Now that your browser knows the website’s IP address, it can load the page.
What is a reverse DNS lookup?
A reverse DNS lookup works the other way around: It’s the process of querying the DNS to figure out a domain name when you already have the IP address.
Why is reverse DNS so important?
Reverse DNS is mostly used for tracking where web traffic and emails come from. Many email servers are configured to reject emails from any IP address that doesn’t have reverse DNS. (More on that later!)
And that’s not the only reason you need reverse DNS.
If you have a website, you’ll have a list of all the IP addresses that have visited your website. When you perform a reverse DNS lookup, you can find the corresponding domain names of everyone who’s visited your website.
This can give you valuable information about where to focus your marketing efforts, who your demographic is, and where most of your web traffic comes from.
Here are seven more ways to use reverse DNS:
- Investigating cybercrime: You can use reverse DNS records to identify threats to your website, e.g. malware spreaders and hackers.
- Email anti-spam: Email spammers tend to give themselves generic, space-filler domains like “www.123thisisawebsite.com.” If you perform a reverse DNS lookup and find that an IP address is connected to a domain name that was clearly selected only as an afterthought, you can save yourself a few headaches by blocking emails from that IP address.
- Analytics and logging: Network monitoring tools usually record information using IP addresses, but they use reverse DNS to record the information in more human-readable terms by using domain names.
- Finding bad server neighbours: If you don’t have dedicated hosting, your website isn’t the only one using the resources of a particular server. Most of the time, websites coexist in peaceful harmony, with no single website hogging the server’s resources, and nobody doing anything illegal and getting blacklisted. But sometimes, this doesn’t happen. Sometimes, one of the websites one your server is used to engage in illegal activity. If this happens, and that website is filtered by an Internet Service Provider, your website and all the other websites on the server will be filtered out, too. If you perform a reverse DNS lookup and find websites with questionable content, you can ask your web host to relocate you to another server. You can also do this to find domain names that are likely to be spam accounts. If these websites are filtered out, yours will be, too. So, if you find a spam account, follow the same protocol: Ask to be moved to another server.
- Checking the legitimacy of people who offer links: Backlinks are great for SEO. Websites rank higher in search results when they’re authoritative enough to have other websites linking to them. Sometimes, website owners will offer you links to boost your SEO. But some people try to cut costs by hosting all their websites on the same IP address. Google demotes links that come from the same IP address, and this would make the links useless for your SEO efforts. A reverse DNS lookup is a quick way of saving yourself the trouble of getting involved with someone who isn’t actually the best person to help with your website ranking.
- Ethical hacking: Ethical hackers can use reverse DNS lookup to determine the vulnerabilities of a website in relation to other websites on the same server. If your website has up-to-date software, but other websites on the same IP address haven’t bother updating, a malicious hacker is likely to move on to an easier target. An ethical hacker can give you the information gleaned from a reverse DNS lookup, so you know how secure your website is likely to be on your current server.
- Checking how many websites your competitors have: If your competitor has a network of connected websites, you can get this information by performing a reverse DNS lookup. This will help keep you from making unwise alliances or from accidentally linking to one of your competitor’s websites.
Reverse DNS can help keep your website safe from email spammers and bad server neighbours, and it can even help you make better marketing decisions and scope out your competitors. This powerful tool is definitely worth knowing about!