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GO Classes DPP | CN | DNS

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Consider the resolution of the domain name www.research.ac.uk by a local DNS resolver using an iterative query mechanism. Assume the resolver's cache is not empty; it already contains the resource record for the .ac.uk name server. No other records are cached. The number of new external DNS query-response pairs the resolver must initiate to find the IP address is $\_\_\_\_$ .

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The iterative process performed by the resolver is as follows:

1. The resolver checks its cache and finds the address for the .ac. uk server. This allows it to skip querying the Root server and the .uk TLD server.

2. Resolver asks the .ac.uk server for www.research.ac.uk. The server replies with the address of the research.ac.uk server. (External Pair 1)

3. Resolver asks the research.ac.uk (authoritative) server for www.research.ac.uk. The server replies with the final IP address. (External Pair 2)

This requires a total of 2 external query-response pairs. (This count does not include the initial query from the user's computer to the local resolver).
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