What is a DNS Cache?

 A valuable reader asks about the DNS Cache in my previous post about clearing the DNS Cache. So I thought it was worthy a post rather than a comment.
So what is DNS. The Domain Name System (DNS) is responsible for translating IP addresses to Domain Names and vice versa. IP address is a number that uniquely identifies a computer on the Internet or network (like your full name uniquely identifies you). For more information about IP address, please see this wikipedia article. As it is easier for the humans to memorize names instead of numbers and the computers deal with numbers rather than names, DNS comes to the rescue which translates names to numbers and numbers to names for the ease of human beings. For example, it is a lot easier to remember www.yahoo.com rather than But actually they correspond to the same system. For confirmation, type either value in the address bar of your browser and you will get the same web page. Most people probably use the DNS server of their ISPs. To see your DNS server, type ipconfig /all in command prompt.
Whenever you type an address in your browser, your system queries your DNS server if it knows about the address. If it does, the server sends back the IP address of the address you typed in your browser otherwise forwards your query to another DNS server for resolution. The process continues until you reach your desired results.
As this process of resolving the IP address gets time consuming, Windows and Linux use a local DNS cache which just saves the corresponding domain names with their IP addresses.  So if the same domain name gets queried again, instead of repeating the DNS resolution process, it consults the local DNS records and gives the results instantly. This improves the DNS resolution process very much. The whole process of DNS resolution is completely transparent to the end user. Sometimes the DNS cache gets corrupted and it has to be cleared which is covered in my previous post about clearing the DNS Cache.





One response to “What is a DNS Cache?”

  1. David Kingsland

    I read that IE7 has a default 30 minute DNS cache, regardless of the DNS TTL. I want to set up a two minute DNS TTL for quick failover, but it looks like I’m wasting my time. Is that so?