Domain Name System - DNS

DNS translates domain names to IP addresses.

What is Domain ?

• domain name is any text or string that you enter in your web page. 
• eg. google.com, etc.

What is IP address ?

• It is a set of protocols that has set of rules that helps millions of devices communicate with each other.
• four set number. eg. 172.25.43.128
• when we say web browser is down, you're not able to access DNS that you're looking for.
• If we use IP address instead of domain name, it will route to the web page

DNS Resolver

• it acts as phone book in this entire thing 

How to bridge the gap b/w human communication, DNS and networking world ?

• In networking word computers use numbers to communicate with each other. 
• In human word we use names to communicate with each other
• Here, DNS resolver acts as phone book, where you search name and match it to number. 
• Ip addresses is a set of protocols that has set of rules that helps millions of devices communicate with each other.
• Thats why we have IP addresses allocated to each and every device on internet.
• All these devices communicate using IP address as unique identifier. 

How DNS Lookup process works ?

    Client : where we enter the website address from web page

• web browser has what we call cache memory. 
• Cache memory stores certain values for a certain time period of time. 
• So, when you enter address abc.com, 
• it first looks in cache memory
• If its a cache miss, then, we forward request to DNS Resolver
• Also, DNS resolver has its own cache 
• If again, its a cache miss, then we route request to ROOT SERVER. 
• Root Server: is top server at top level in DNS hierarchy. 
• Let, root server still don't have information of abc.com that you're looking for
• Root server has information about Top level domain server that you have to route your request to. 
• Also, Root servers are placed across different locations, throughout the world.
• There are 12 different organizations that manage these root servers.
• Root server provides the top level domain server IP address.
• Then, we send request to Top Level Domain server.
• TLD is nothing but "Top Level Domain" which basically means it has all the information for the top level domain. 
• In our case TLD will be ".com".
• Now let TLD also, dont have IP address of abc.com, but it then send the request to Authoritative Name Server
• Authoritative Name Server, has all the information and all the DNS records that we need to access 
• It renders the DNS record that we need to access, and sends back the IP address.
• Not DNS resolver store IP address in it's cache and send it back to web browser.
• Now, since, web browser has IP address, then it sends the request using IP address to web server.
• Now Web Server has all the content that needed to display in your web page. 
• What we render back is content of web page.