Domain Name System

DNS (Domain Name System): frequently asked questions

Applies to Windows Vista

Here are answers to some common questions about DNS.

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What is DNS (Domain Name System)?

Websites have both a "friendly" address, called a Uniform Resource Locator (URL) and an IP address. People use URLs to find websites, but computers use IP addresses to find websites. DNS translates URLs into IP addresses (and vice versa). For example, if you type http://www.microsoft.com into the address bar in your web browser, your computer sends a request to a DNS server. The DNS server translates the URL into an IP address so that your computer can find the Microsoft web server.

What is the last part of a URL?

The last part of a URL is called a top-level domain name (TLD). TLDs identify different types of websites. Here are some common TLDs and what they stand for:

Top-level domain	Stands for
.com	commercial (business) site
.net	Internet administrative site
.org	nonprofit organization
.gov	U.S. government agency
.edu	educational institution

In addition to the TLDs listed above, individual countries or regions have their own TLDs. For example, .ca is the TLD for Canada.

What is DNS dynamic update?

Some computers are given a different IP address each time they connect to the Internet. An Internet service provider (ISP) can use a few IP addresses to serve many customers that way, but it means that your computer's "address" on the Internet is always changing. If you host a website, you don't want the website name to change, even if your ISP changes the IP address. DNS dynamic update automatically maintains the relationship between your fixed website name and the changing IP address so that your website is easy to find on the Internet.

How do I look up a DNS name or IP address?

You must be connected to the Internet to look up a DNS name or IP address.

1. Open the Command Prompt window by clicking the Start button , clicking All Programs, clicking Accessories, and then clicking Command Prompt.
2. At the command prompt, type nslookup, a space, and the IP address or domain name (for example, nslookup microsoft.com), and then press ENTER.

What is the DNS cache?

When you type a web address into your web browser and press ENTER, you are sending a query to a DNS server. If the query is successful, the website you want opens; if not, you'll see an error message. A record of these successful and unsuccessful queries is stored in a temporary storage location on your computer called the DNS cache. DNS always checks the cache before querying any DNS server, and if a record is found that matches the query, DNS uses that record instead of querying the server. This makes queries faster and decreases network and Internet traffic.

How can I see the contents of the DNS cache?

1. Open the Command Prompt window by clicking the Start button , clicking All Programs, clicking Accessories, and then clicking Command Prompt.
2. At the command prompt, type ipconfig /displaydns.

How can I clear the DNS cache?

Clearing the DNS cache forces DNS to query a DNS server rather than using information stored in the cache. You might want to clear the DNS cache if you are moving and changing websites, or if you are receiving repeated errors when you know the web address you are typing is correct.

1. Open the Command Prompt window by clicking the Start button , clicking All Programs, clicking Accessories, and then clicking Command Prompt.
2. At the command prompt, type ipconfig /flushdns.