Domian Naming System

Introduction:

• Used to resolve human readable hostnames(www.google.com) to machine-readable IP addresses(204.13.248.115).

• Provides information about domain name such as mail services.

Why is DNS important?

• DNS is like a phone book for Internet.

• DNS matches domain names to thier respective IPs on internet.

• When a URL is entered in browser, CPU uses DNS to retrieve the website's IP address.

• IP address, instead of domain name is used to access webpage, if there is no DNS.

                                  



 How does DNS work?

• While accessing a website, computer follows a series of steps for turn a domain name into IP address.

• This process is common every time you use a domain name.

Step 1: Request information

• Request is sent to the CPU with the domain name.

• It looks at local DNS cache, which stores the recently retrieved information.

• Otherwise transfers to DNS Server in the form of query.

Step 2: Ask the recursive DNS servers

• CPU sends a query to DNS server of Internet Service Provider which are called as Recursive servers.

• Recursive servers also have DNS cache which can also used to store rescent information.

• If not, then they query root name servers.

Step 3: Ask the root nameservers

• Name server is a computer answers about domain names and IP addresses.

• 13 root nameservers act as a telephone switchboard for DNS.

• They don't know answer, but can redirect to the one who know where to find the answer.

Step 4: Ask the TLD nameservers

• Root nameservers direct the query to Top Level Domains(TLD).

• TLD servers don't have the information needed but refer to server that knows information.

• Example of TLDs are .com, .in, .us, .gov, .org etc.,

Step 5: Ask the authoritative DNS servers

• Authoritative nameservers are responsible for knowing all the information about specific domain.

• Data is stored in the form of DNS records.

• Records store information can be of any type, but requested information (IP address) is sent.

Step 6: Retrieve the record

• Recursive server retrieves record and stores in its local cache.

• If another request for same website(google.com) is recieved, then again no need to go through this process again.

• Records have a time-to-live period(same as expiration date) to be in cache.

Step 7: Receive the answer

• Recursive server returns record to requested computer CPU.

• Then CPU stored the record in its Cache and reads the IP address from the record and passes to browser.

• Browser opens connection to webserver and retrieves the webpage.

This entire process, from start to finish, takes only milliseconds to complete.