. Stands for Domain Name System.
. We can simply communicate to various websites using domain names like yahoo.com and google.com etc.
. But computers are addressed with numbers called IP addresses.
. To bridge communication gap between users and computers, DNS resolves domain names to IP addresses.
. We can simply communicate to various websites using domain names like yahoo.com and google.com etc.
. But computers are addressed with numbers called IP addresses.
. To bridge communication gap between users and computers, DNS resolves domain names to IP addresses.
Why is it important?
. It acts like phone book. If we don't know person's number but only their name, we look up in phone book using their names.
. If DNS is not there, we would have to view websites using IP Address instead of names which is very complicated.
How it Works?
Step 1:
. When you type any website name in browser, your computer looks in it local DNS cache.
. Local DNS cache stores information that your computer already retrived.
. If it founds, it returns IP Address and computer connects to that website.
. If not found, it sends query to next level called Resolver Server.
Step 2:
. Resolver server is basically ISP (Internet Service Provider) server.
. When it receives query, it will check in its cache memory to find IP Address.
. If not found, it sends query to next level called Root Server.
Step 3:
. Root Servers are top or root of DNS hierarchy.
. There are 13 sets of root servers strategically placed around world.
. Operated by 12 different organizations.
. When it receives query from resolver, it doesn't know IP address.
. But it knows to direct resolver to find IP address.
. It directs resolver to Top Level Domain (TLD) for .com domain.
Step 4:
. Resolver sends query to TLD server which is directed by Root Server.
. TLD server stores address information of all top level domains like .com , .org and .in etc.
. This particular TLD server manages .com domain addresses.
. It doesn't know IP Address requested by resolver but it directs to final level called Authoritative name servers.
Step 5:
. Now Resolver sends query to Authoritative Name Servers.
. These are responsible for knowing everything about domain which includes IP Address.
. So when it receives query for any domain like abc.com, it responds with IP address.
. Now finally, Resolver can tell your computer the IP address for abc.com.
Note:
. Once Resolver receives IP Address, it stores it in the local cache memory so that it doesn't need to repeat all process again.
. Entire process from start to finish takes only milliseconds to complete.
. Entire process from start to finish takes only milliseconds to complete.
Types of DNS servers:
. Basically there are two types of DNS servers called Primary and Secondary servers.
. They are the DNS server computers which store domain names.
. Information in both the servers are identical.
. Values for these DNS servers are assigned by Internet Service Provider (ISP).
. It is not sure that a single DNS server can function all the time. So there are 2 servers.
Primary DNS server:
. When setting up a DNS server, server admin has choice to designate a server as primary or secondary.
. It is referred as Master server.
. In some cases, Primary server can act as secondary server for another zone.
. It contains information like IP address of domain and who is responsible for that domain.
. Changes to zone files can only be done in primary servers.
Secondary DNS server:
. It is referred as slave server.
. A single zone can contain only one primary server but it can have multiple secondary DNS servers.
. It takes information from the primary server automatically.
. It functions as read-only server.
. Cannot make any changes to the zone files but information is updated from Primary server through zone transfer.
. It just functions as a back up server when Primary server is not working.
Finding your Primary and Secondary DNS server address:
. Admins setup primary and secondary DNS servers.
. We can find out what primary and secondary DNS servers we are using by getting into router configuration.
. Browse Router IP in the browser and login with credentials.
. In the status bar, we can find the Primary and Secondary DNS server IP addresses.
