DNS Name Resolution Mechanism

DNS name resolution allows Internet resources to be accessed by using domain names rather than IP addresses. To resolve domain names into IP addresses, DNS servers coordinate their efforts in a hierarchical and distributed manner.

In order to enable Internet communication, DNS (Domain Name System) name resolution translates domain names into IP addresses. Here is an overview of the DNS name resolution mechanism:

•  When a machine's application attempts to resolve a name, it contacts the operating system's resolver component.
•  To access a site, the system first checks its local DNS cache to see if the domain name and IP address mapping is already stored. If this is the case, the system does not have to query the DNS again to access the site.
•  If the domain name cannot be found in the local cache or in the network settings, the system contacts the local DNS server. The local DNS server is typically managed by the Internet Service Provider (ISP) or network administrator.
•  A local DNS server can query the root DNS servers for authoritative DNS servers, which are located on top-level domains (TLDs), such as ".com," ".org," ".net.", etc.
•  In order to determine the mapping between a domain name and an IP address, the local DNS server queries the authoritative DNS server.
•  As soon as the authoritative DNS server responds, it sends the responses to the local DNS server, which then forwards them to the requesting system.
•  In order to speed up future queries for the same domain, DNS resolution results are cached at various levels, from the local cache to the cache of the local DNS server.
•  The IP address associated with the domain name can now be used to access a website or service.

Here is an example of resolving the domain name www.techmentor.com

1. A client asks its reference server (Internet Service Provider or local server): "What is www.techmentor.com's address?"
2. Local server to root server: "Give me the address of the server that knows the com zone."
3. "Well, the server at 192.170.30.2 can help you. It has information for the com zone."
4. Give me the address of a server that knows the techmentor.com zone.
5. This is the server at the address 162.144.1.10 that can assist you."
6. "Do you have a www record in your techmentor.com domain?" asked the local server to the zone server for techmentor.com.
7. The IP address of the techmentor.com zone server is 162.144.1.46.
8. The client station's local server: "The IP address of www.techmentor.com is 162.144.1.46."