Question
Consider the resolution of the domain name www.gate.org.in by a DNS resolver. Assume that no resource records are cached anywhere across the DNS 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_____________.
Official answer and solution
- Official answer
- 4
- From
- Official GATE 2022 answer key
Solution
Trace the step-by-step iterative DNS hierarchy queries from the root server down to the authoritative domain server.
Under iterative DNS resolution with an empty cache:
- Pair 1: The resolver queries the Root DNS server ('.'). The root server replies with a referral to the Top-Level Domain (TLD) server for '.in'.
- Pair 2: The resolver queries the '.in' TLD server. The '.in' server replies with a referral to the authoritative server for 'org.in'.
- Pair 3: The resolver queries the 'org.in' server. The 'org.in' server replies with a referral to the authoritative server for 'gate.org.in'.
- Pair 4: The resolver queries the 'gate.org.in' server for the address of 'www.gate.org.in'. The server replies with the final A-record (IP address).
Thus, exactly 4 query-response pairs are involved.
4
Assuming 'www' is a separate domain zone requiring a 5th query rather than an A record in 'gate.org.in'.
The answer is the one in the official GATE answer key. The solution is this site's own explanation.
Source
- Paper
- GATE 2022 Computer Science and Information Technology (CS)
- Question
- 35 of 65
- Section
- Computer Science and Information Technology
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