askvity

What is DNS in application layer protocol?

Published in Networking Protocols 4 mins read

DNS (Domain Name System), as an application layer protocol, translates human-readable domain names (like google.com) into IP addresses (like 142.250.184.78) that computers use to identify each other on the internet. It's essentially the internet's phonebook.

DNS Functionality Explained

Here's a breakdown of how DNS works within the application layer:

  • Application Layer Protocol: DNS operates at the application layer of the TCP/IP model. This means it interacts directly with applications like web browsers, email clients, and other software that need to access resources on the internet.
  • Name Resolution: The core function of DNS is name resolution. When you type a domain name into your browser, the browser uses the DNS protocol to send a query to a DNS server.
  • Recursive and Authoritative Servers: The query typically goes to a recursive DNS server (often provided by your ISP). If the recursive server doesn't know the IP address, it queries authoritative DNS servers, which hold the definitive records for specific domains.
  • Resource Records (RRs): DNS servers store information in resource records. These records contain various types of data, including:
    • A (Address) Records: Map a domain name to an IPv4 address.
    • AAAA (Quad-A) Records: Map a domain name to an IPv6 address.
    • CNAME (Canonical Name) Records: Create an alias for a domain name.
    • MX (Mail Exchange) Records: Specify the mail servers responsible for accepting email messages for a domain.
    • NS (Name Server) Records: Delegate a DNS zone to a specific set of authoritative name servers.
  • Caching: To improve performance, DNS servers cache the results of previous queries. This reduces the need to repeatedly query authoritative servers. The TTL (Time To Live) value in each resource record determines how long a server can cache the record.
  • Hierarchical Structure: DNS is organized in a hierarchical structure, similar to a file system. The root zone is at the top, followed by top-level domains (TLDs) like .com, .org, and .net. Each TLD is managed by a registry, which delegates authority to registrars and domain owners.

Example Scenario

  1. You type www.example.com into your web browser.
  2. Your browser sends a DNS query to your configured DNS resolver (usually your ISP's server).
  3. The resolver checks its cache. If the information isn't cached, it starts a recursive query.
  4. The resolver queries the root DNS servers, which direct it to the authoritative name servers for the .com TLD.
  5. The .com name servers direct the resolver to the authoritative name servers for example.com.
  6. The example.com name servers respond with the IP address associated with www.example.com (an "A" record).
  7. The resolver caches this information and sends the IP address back to your browser.
  8. Your browser uses the IP address to connect to the web server hosting www.example.com.

Key Advantages

  • User-Friendliness: Allows users to access websites and services using easy-to-remember domain names instead of complex IP addresses.
  • Scalability: The hierarchical structure enables the internet to scale to accommodate billions of devices and domain names.
  • Flexibility: Allows for changes to IP addresses without requiring users to update their bookmarks or configurations.
  • Reliability: Redundancy and caching mechanisms ensure that DNS services are available even if some servers fail.

Related Articles