What is DNS?
DNS is an acronym for Domain Name System.
Very simply it is the mechanism that converts domain names to IP addresses.
DNS was invented because computers talk to each other by ip address and people don’t want to remember IP addresses.We don’t want to go to internetworks.net by typing http://184.108.40.206 or some other IP address string, we want to go there by typing http://internetworks.net/ and let DNS translate it for us in the background. It also helps by allowing that computer at that IP address answer to several domain names.
Computers on the Internet talk to others by referring to their IP address, not their domain name. It’s not obvious, but there is a necessary translation to IP address for every request for something from a domain name. Lets start first with a discussion of IP addresses. Decimal numbering of an ip address looks like this: nnn.nnn.nnn.nnn where nnn is any decimal number between 0 and 255. It is referred to as the dotted quad. All computers on the Internet have IP addresses.
When you set up a domain name, you specify one or more DNS servers that are “authoritative” for that domain name. Then the DNS admin sets up several entries for that domain name:
- domain.name to IP address
- www.domain.name to the same as the domain.name
- mail.domain.name to the IP address of the mail server for that domain
- IP address to domain.name (called the reverse entry) for each entry and important for mail to work reliably.
Let’s understand this by example. What happens when we type an address, http://www.internetworks.net in our browser (I.E. or Firefox or Opera for example)
- First a program has to find out what the ip address is:
- Your computer asks your DNS server to give your computer the IP address.
- Is the request for a .com, .net, .org, .biz, etc.
- Ask the ‘top level domain name servers’ that are responsible for .net’s what DNS server is responsible for internetworks.net. The answer is an ip address and the name ns1.oknet.com.
- Ask ns1.oknet.com what is the IP address of internetworks.net. The answer is an ip address.
- Your DNS server caches the answer for subsequent questions for a period of time.
- Ask the server at the ip address in the previous step for the default page for internetworks.net. Get the page.
- Followup requests for images and other things referred to on the page.
All of this DNS stuff goes on in the background and normally doesn’t cause problems. It can be ignored for the most part unless you are an administrator of some systems involved in it.
One of the most likely problems you might see with DNS is an overloaded ISP DNS server. Watch your “status bar” when you access the Internet with your Browser. If you see lots of messages to the effect ‘looking up domain.name’ then your DNS server is overloaded. Talk with your ISP about alternative DNS servers and you may really improve your access to web pages.
Feel free to ask questions about this as we have really only scratched the surface of DNS here.