DNS

Networks

How a Domain Name Server Functions

A Domain Name Server (DNS) is a distributed database system that translates human-readable domain names (e.g., `www.example.com`) into machine-readable IP addresses (e.g., `192.0.2.1`). This process allows users to access websites and services without needing to remember numeric IP addresses.

Key Components of DNS

1. Root Name Servers: The top-level servers that respond to queries for domain name resolution by directing requests to the appropriate top-level domain (TLD) name servers (e.g., `.com`, `.org`, `.net`). 2. TLD Name Servers: These servers store information about authoritative name servers for domain names within a specific TLD. 3. Authoritative Name Servers: These servers hold the actual IP address information for specific domain names. 4. Recursive Resolvers: These servers act as intermediaries that query other DNS servers on behalf of the client to resolve domain names.

Recursive Nature of DNS

The DNS query process is recursive, meaning the recursive resolver handles all necessary queries to provide the client with the final result. The resolver queries multiple servers in sequence until the IP address is found, caching the results at each step to improve performance for future requests.

Example of a DNS Query

When a user enters `www.example.com` into their web browser, the following steps occur:

1. Local DNS Cache:

  The browser first checks the local DNS cache to see if it has a cached IP address for `www.example.com`. If found, it uses the cached IP and skips the following steps.

1. Query to Recursive Resolver:

  If the local cache is empty, the query is sent to a recursive resolver (e.g., provided by the user's ISP or a public DNS like Google DNS or Cloudflare).

1. Query to Root Name Server:

  The recursive resolver queries a root name server to find the TLD name server for `.com`. The root server responds with the address of the `.com` TLD name server.

1. Query to TLD Name Server:

  The recursive resolver queries the `.com` TLD name server to find the authoritative name server for `example.com`. The TLD name server responds with the address of the authoritative name server.

1. Query to Authoritative Name Server:

  The recursive resolver queries the authoritative name server for `example.com`, which responds with the IP address for `www.example.com`.

1. Response to Client:

  The recursive resolver returns the IP address to the client (e.g., the browser), which then connects to the web server at that IP address.

1. Caching:

  Each server involved in the process may cache the result to optimize future queries. For instance:
  * The recursive resolver caches the result to quickly answer subsequent queries for `www.example.com`.
  * The client device may also cache the result locally for a limited time.

Summary of DNS Workflow

1. Browser checks local DNS cache. 2. Query sent to a recursive resolver. 3. Recursive resolver queries:

  * Root name server → TLD name server
  * TLD name server → Authoritative name server
  * Authoritative name server → Final IP address

4. Recursive resolver returns the result to the client. 5. Caching occurs at various levels to improve performance.

This recursive and distributed nature ensures DNS is highly efficient and resilient.

Standards

These standards are used from the IB Computer Science Subject Guide

• Describe how a domain name server functions.

a group or system of interconnected people or things.

Give a detailed account or picture of a situation, event, pattern or process.