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Explain the purpose of DNS.

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DNS, or Domain Name System, is a fundamental technology used on the Internet to translate human-readable domain names into IP addresses. It serves as a distributed hierarchical database that enables the mapping of domain names to IP addresses, allowing users to access websites and other resources using familiar, easy-to-remember names rather than numerical IP addresses.

Here's a detailed technical explanation of the purpose of DNS:

  1. Address Resolution:
    • When you enter a domain name (like www.example.com) into a web browser, your device needs to know the corresponding IP address to establish a connection with the server hosting that website.
    • DNS acts as a distributed directory service that resolves these domain names to their associated IP addresses.
  2. Hierarchical Structure:
    • The DNS system is organized in a hierarchical structure, consisting of multiple levels called domain levels or labels. The top-level domain (TLD) is at the highest level, followed by second-level domains (SLD) and subdomains.
    • For example, in www.example.com, ".com" is the TLD, "example" is the SLD, and "www" is a subdomain.
  3. DNS Servers:
    • DNS uses a distributed system of servers to handle the translation of domain names into IP addresses. These servers are categorized into different types, including authoritative name servers, recursive resolvers, and root servers.
    • Authoritative name servers store specific domain information, while recursive resolvers handle user requests by recursively querying other servers until the final IP address is found.
  4. DNS Query Process:
    • When you type a domain name in your browser, your device sends a DNS query to a local DNS resolver (often provided by your ISP or configured manually).
    • If the resolver has the IP address in its cache (a stored record of recent DNS queries), it returns the result. Otherwise, it starts the DNS resolution process.
  5. Iterative vs. Recursive Queries:
    • DNS queries can be iterative or recursive. In an iterative query, the resolver asks each server in sequence until it finds the IP address. In a recursive query, the resolver delegates the task to other servers and waits for a complete answer.
    • Recursive queries are more common in typical user scenarios, making the process more efficient.
  6. Caching:
    • To reduce the load on DNS servers and speed up future queries, DNS resolvers cache the results of previous queries. This caching mechanism helps improve overall system performance by avoiding redundant queries for frequently visited sites.