GATE CS 2022 Q25 — Application Layer Protocols: DNS, SMTP, HTTP, FTP, Email

To resolve the domain name www.gate.org.in using an iterative query mechanism with no caching, the DNS resolver queries the DNS hierarchy step-by-step starting from the root.

The domain hierarchy for www.gate.org.in is structured as follows:

$\text{Root (.)} \rightarrow \text{.in} \rightarrow \text{org.in} \rightarrow \text{gate.org.in} \rightarrow \text{www.gate.org.in}$

The DNS resolver performs the following query-response pairs:

1. Pair 1: The resolver queries the Root DNS server for www.gate.org.in. The Root server responds with the referral (IP address) of the .in TLD server.
2. Pair 2: The resolver queries the .in TLD server. The TLD server responds with the referral of the org.in DNS server.
3. Pair 3: The resolver queries the org.in DNS server. This server responds with the referral of the authoritative DNS server for gate.org.in.
4. Pair 4: The resolver queries the authoritative DNS server for gate.org.in. This server responds with the final IP address of www.gate.org.in.

Thus, the total number of DNS query-response pairs involved in completely resolving the domain name is 4.