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Domain Name System (DNS)

Updated Jan 16, 2019 ·

Overview​

The Domain Name System (DNS) is a hierarchical system that translates human-readable domain names (like example.com) into IP addresses (like 192.168.1.1) that computers use to identify each other on a network.

  • DNS makes it easier for users to access websites without remembering numerical IP addresses
  • It consists of a distributed database that is queried to resolve domain names into IP addresses
  • DNS functions over UDP port 53, allowing quick and efficient queries

As an example, when you type www.wikipedia.org into your browser, DNS translates this domain name into the IP address needed to reach Wikipedia's servers.

How DNS Works​

  1. A user enters a domain name (e.g., www.wikipedia.org) into their web browser.
  2. The browser sends a request to the DNS resolver, often provided by the user's ISP.
  3. The DNS resolver queries the root DNS server to find the top-level domain (TLD) server (e.g., .org).
  4. The TLD server directs the resolver to the authoritative DNS server for wikipedia.org.
  5. The authoritative DNS server provides the IP address for www.wikipedia.org.
  6. The resolver returns the IP address to the browser, which then connects to the website.

DNS Servers​

DNS servers are critical components of the DNS infrastructure, responsible for storing domain name records and resolving queries.

  • Root Servers: The top level of the DNS hierarchy, directing queries to the appropriate TLD servers
  • TLD Servers: Responsible for handling top-level domains (like .com, .org) and directing queries to authoritative servers
  • Authoritative Servers: Store the actual DNS records for a domain, providing the IP addresses when queried

dig​

The dig (Domain Information Groper) command is a tool used to query DNS servers and troubleshoot DNS issues. It provides detailed information about DNS queries and responses.

Example: Running dig wikipedia.org will query the DNS for the domain wikipedia.org and return detailed information.

$ dig wikipedia.org

; <<>> DiG 9.16.1-Ubuntu <<>> wikipedia.org
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 62636
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; QUESTION SECTION:
;wikipedia.org.               IN      A

;; ANSWER SECTION:
wikipedia.org.        3600    IN      A       208.80.154.224

;; Query time: 22 msec
;; SERVER: 192.168.1.1#53(192.168.1.1)
;; WHEN: Tue Aug 27 12:34:56 UTC 2024
;; MSG SIZE  rcvd: 65

Explanation:

  • Header: Displays general information like query type and status
  • Question Section: Shows the query made (e.g., wikipedia.org for an A record)
  • Answer Section: Provides the IP address associated with the domain
  • Query Time: The time it took to receive a response
  • Server: The DNS server that responded to the query