Skip to main content

Short note: DNS

Short answer

DNS is a distributed hierarchical database translating domain names to IP addresses, using port 53 (UDP/TCP). Hierarchy: root, TLD, authoritative, and local resolver servers. Key records: A (IPv4), AAAA (IPv6), NS (name server), CNAME (alias), MX (mail server), PTR (reverse), SOA (zone info). Resolvers query iteratively, caching results per TTL.

Write a short note on DNS (Domain Name Server).

DNS (Domain Name System) is a distributed hierarchical database that translates human-readable domain names (www.tu.edu.np) into IP addresses (and the reverse). It runs on port 53, normally on UDP (TCP for zone transfers and large replies). The server software is called a name server.

Hierarchy

              . (root)
        /       |       \
      com      org      np  (TLD)
                       /  \
                    edu    com
                    /
                   tu   -> www.tu.edu.np

Types of name servers

  • Root servers: know the TLD servers (13 root server addresses, many anycast copies).
  • TLD servers: .com, .org, .np ...
  • Authoritative servers: hold the real records of a domain.
  • Local (resolver) server: the ISP's server that the host queries; it caches answers.

Working

The host's resolver asks the local DNS server. If the answer is not cached, the local server queries the root, TLD and authoritative servers in turn and returns the IP address. Answers are cached for the time given by their TTL.

Main records

A (IPv4), AAAA (IPv6), NS (name server), CNAME (alias), MX (mail server), PTR (reverse lookup), SOA (zone info).

Services: host name translation, mail server lookup, load distribution, host aliasing.

✓ Answer checked by Claude Opus 5.5 (high effort)

Related questions

All Computer Networks and Security chapter 6 questions →