DNS resolver

• When a user enters a domain like www.wikipedia.org in the browser, the DNS resolution process begins to convert that human-readable name into an IP address.
• First, the system checks locally within the machine, including the browser cache and OS cache, to see if it already knows the IP.
• If not found, a DNS query is initiated through the local resolver, which acts as the starting point.
• This resolver forwards the request to the ISP’s resolver.
• The ISP resolver again checks its cache, and if the IP is still not available, it begins the hierarchical lookup process.
• It first contacts the Root Name Server, which directs the resolver to the Top-Level Domain (TLD) server based on the domain extension, such as .org, .com, or .in.
• For wikipedia.org, it points toward the .org TLD server.
• The resolver then contacts zone file, which holds all the DNS records such as A records (for IPv4), AAAA records (for IPv6), CNAME (aliases), and MX (mail routing).
• From this zone file, the correct IP address corresponding to www.wikipedia.org is retrieved.
• This IP is then sent back step by step from the zone file to the TLD server, then to the ISP resolver, then to the local resolver, and finally to the browser.
• Once the browser receives the IP address, it can initiate a connection to the actual server using protocols like TCP and send the HTTP request.
• This entire DNS resolution process ensures that a simple domain name is accurately mapped to its correct server location on the internet.