Skip to main content

Starter Notes

Updated Jan 16, 2018 ·

Overview​

The Domain Name System (DNS) converts easy-to-remember domain names (like example.com) into IP addresses (like 192.168.1.1) that computers use to locate each other.

  • Lets users access websites without remembering IP numbers
  • Uses a distributed database to map names to addresses
  • Works mainly over UDP port 53 for fast lookups

Example: Typing www.wikipedia.org in a browser triggers DNS to find the IP address for Wikipedia’s servers.

How DNS Works​

  1. User enters a domain name in a browser.
  2. Browser sends the request to a DNS resolver (usually from the ISP).
  3. Resolver contacts a root DNS server to find the TLD server (e.g., .org).
  4. TLD server points to the authoritative server for the domain.
  5. Authoritative server returns the IP address.
  6. Resolver sends the IP to the browser, which connects to the website.

DNS Servers​

DNS servers store records and answer queries.

  • Root servers

    • Top of the DNS hierarchy
    • Point to TLD servers

  • TLD servers

    • Manage top-level domains (e.g., .com, .org)
    • Point to authoritative servers

  • Authoritative servers

    • Store DNS records for domains
    • Provide IP addresses when asked

dig​

The dig (Domain Information Groper) is 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

Three Main Functions of DNS​

  • Name resolution

    • Translates domain names into IP addresses
    • Enables devices to locate each other
    • Most common use of DNS

  • Namespace

    • Organizes how domain names are structured
    • Defines valid formats and characters
    • Guides how names are interpreted

  • Name registration

    • Assigns unique domain names
    • Prevents duplication of names
    • Managed by registration authorities