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DNS (Domain Name System)

  • Maps a domain name to an IP address.

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DNS Resolution Steps​

  • The browser (client) checks if the hostname to IP address mapping exists in its local cache.
  • If not found, the client checks the Operating System (OS) local cache via a system call.
  • If still not found, the client makes a DNS request to the Gateway/Router and checks the router's local cache.
  • If unsuccessful, the router forwards the request to the Internet Service Provider (ISP) and checks the ISP's DNS cache.
  • If the mapping is still not found, the DNS resolver queries the root servers (13 root servers with replicas worldwide).
  • The DNS resolver then queries Top Level Domain (TLD) servers (e.g., .com, .org) and Authoritative name servers (e.g., google.com).
  • Optionally, the DNS resolver may query Authoritative subdomain servers (e.g., maps.google.com) depending on the query.