Consider the resolution of the domain name www.mydomain.com by a resolver. Assume that no resource records are cached anywhere across the servers and that iterative query mechanism is used in the resolution. The number of DNS query-response pairs involved in completely resolving the domain name is ___.

GATE 2022 · Computer Networks · Application Layer Protocols · medium

Answer: 4 DNS query-response pairs are involved in completely resolving www.mydomain.com.

1. Identify DNS hierarchy levels for www.mydomain.com: The domain www.mydomain.com requires resolution through: - Root DNS server (knows .com TLD server address) - .com TLD server (knows mydomain.com authoritative server address) - mydomain.com authoritative server (knows the IP of www.mydomain.com)
2. Count query-response pairs in iterative mode: Q1: Client -> Local Resolver (query: what is www.mydomain.com?) Q2: Local Resolver -> Root DNS (iterative query) Q3: Local Resolver -> .com TLD DNS (iterative query with root's referral) Q4: Local Resolver -> mydomain.com authoritative DNS (iterative query with TLD's referral) Resolver returns final answer to client (part of Q1's response). Total = 4 query-response pairs.