Consider the resolution of the domain name www.gate.org.in by a DNS resolver.…
2022
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_____________.
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Correct answer: 4
Key idea: iterative DNS resolution issues one query to each level of delegation plus a final query to the authoritative server for the name being resolved.
Step 1: The resolver queries a root server for www.gate.org.in and gets a referral to the .in nameservers.
Step 2: The resolver queries a .in nameserver for www.gate.org.in and gets a referral to the org.in nameservers (the second-level domain under .in).
Step 3: The resolver queries an org.in nameserver for www.gate.org.in and gets a referral to the authoritative nameserver for gate.org.in.
Step 4: The resolver queries the authoritative nameserver for gate.org.in for the A record of www.gate.org.in and receives the answer.
Therefore, with no caching and using iterative queries, four query–response pairs are needed to fully resolve www.gate.org.in.
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