If you’ve read the WHT article: What is DNS? DNS in Plain English, you know a little about DNS. You may have heard the term “Domain Masking” or “Shadowing” when you’ve bought a new domain.

What is Domain Masking?

Domain Masking is sometimes called a “pointer domain.” If we are to continue our example of a postal system mentioned in DNS in Plain English, is like having your mail sent to a P.O. Box. It’s not a physical address, and the “final” destination is another location entirely. You’re hiding the final address from the sender for whatever reason.

Domain Masking is usually offered by your domain registrar as a service. [How is this different from Domain Forwarding? Read Domain Forwarding in Plain English]

If you set up Domain Masking for a blogspot blog, for example, you might consider the following:

http://www.domainname.com is a Domain Mask for domainname.blogspot.com

When someone types in http://www.domainname.com, it’s really forwarding to domainname.blogspot.com without the address changing in the address bar (the part of your browser where you see the URL beginning with “http://…”. The user continues to see http://www.domainname.com in the address bar although the site and its contents are really from domainname.blogspot.com.

Why Use Domain Masking?

If you have an existing site that is being hosted free (like a blog from Blogger or WordPress.com) being able to give out a short URL or address may be a benefit to you. Also, if you’re not ready to pay for hosting, it’s a quick way to utilize your domain name.

Why Should I Think Twice about Domain Masking? Does it Matter?

It definitely matters to Google. If you will rely on search engines for any traffic, then you need to seriously consider if you need to use domain masking or if you can find another solution, such as Domain Forwarding or Switching Your Web Hosting.

Google doesn’t like duplicate content, and with Domain Masking, it sees two domains with the same exact content. What will happen? Google has not released their exact policy on Domain Masking but they make it clear that duplicate content will only get indexed once, and it may not the URL or domain that you prefer.

I Still Want to Use Domain Masking. What Do I Do?

Make sure you use 301 (Permanent) Redirects if given a choice by your domain management.

It may be possible to do this in the settings when you select Domain Masking, or it may require access to the administrative console of the server, so it’s possible that this will not be available to you.

Ready for More? More Resources on Domain Masking:

• What is DNS? DNS in Plain English [When I Have Time]
• Domain Masking [Wikipedia]
• Webmaster Guidelines and Duplicate Content [Google Help]
• Will Domain Masking Impact my SEO? [Your SEO Plan]

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 DNS, or Domain Name System, is the backbone that runs the Internet. Without it, http://www.google.com would have no meaning to anyone.

When you type http://www.google.com into your browser, how does it end up at the simple search interface we know and love? When you type in a web address, the part after “http://” and before the first “/” is considered to be the domain of the page.

DNS is very similar to the postal or telephone addressing system most countries have, with two main components: a name, and a more detailed, numerical address. If you’re sending a letter to someone, say, Jennifer who lives in Manhattan, you’d address it such:

Jennifer Johnson

100 5th Avenue

New York, NY 10027

With the Internet, the “name” is called a domain, and the “numeric address” part is an IP (Internet Protocol) address. But unlike sending a letter, as a regular user on the Internet, you don’t have to know the numeric address of your site, just the domain name!

Each domain (in the form of http://www.domainname.com) has a specific IP address it corresponds to. This IP address indicates the “home” or server where the image or web page being requested is being housed.

DNS: The IP Address

The IP address has the following general format:

xxx.xxx.xxx.xxx – where each ‘xxx’ is a number from 0-255.

If you have a dedicated IP address, there will be only one domain at your “house” address. Very few commercial hosting options offer dedicated IPs with their basic plans, and usually there are hundreds to thousands of domains being addressed to the same server. So your address is more likely to be an apartment building instead of a single-family house.

The format of DNS with regard to IP addresses is simple, and in this article, we’ll focus on just one type of DNS entry – for the website. In a “DNS Address Book” you’d see the following: domain name IN A IPAddress.

http://www.google.com IN A 209.85.129.99 (for this example, google.com’s IP Address)

DNS Name Servers: Your Global Directory Assistance

Another important player in this DNS world is the “name server” which is the equivalent of your local post office. They know where you live and that when a letter arrives with your name and address, they confirm and ensure that it reaches its final destination.

Each domain has just one name server that is in charge of keeping that domain’s information and IP addresses. Simply, when your change your IP address or “home,” your domain’s name server passes the word on the internet (with the help of routers, which we’ll talk about later) to the rest of the internet so a request directed to your website will find you.

What Happens When You Change Web Hosting

{Read WHT article: How to Buy a Domain and What to Do with It} If you were moving your physical house, you’d have to notify the local post office or city hall with your new address. With your website, since you’re moving your data from one “house” to another, you need to update your site’s address, too. Usually this will require you changing the IP address to reflect the new hosting company’s server where your information will reside. Your hosting company can provide the correct IP address for you.

• In the DNS, you’ll delete the current “address” and then insert the new IP address of your new hosting.
• The name server notices that the DNS for your domain has changed, and usually within 24-48 hours, the name server will notify the rest of its network, which in turn will propagate the information throughout the internet.
• The next time someone types in http://www.domainname.com, the request will be sent to your new adddress!

Advanced DNS Questions

• Can you have multiple IP addresses for a single domain? Yes, much like Lifestyles of the Rich and Famous, sites which are very popular often have multiple “houses” – and often this is done with sites that have a lot of traffic and are using multiple servers to meet the demand.
• Can multiple domains respond to the same (IP) address? Yes, as mentioned above, many commercial hosting solutions offer low-priced hosting because they can put hundreds or thousands of sites/domains on the same server since the traffic demands are so low. Depending on the traffic that comes to your site, you’ll probably never notice.

Ready for More? More Resources on DNS

• WHT article: How to Buy a Domain and What to Do with It
• Wikipedia: DNS
• Webopedia: DNS
• How Stuff Works: DNS