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Consider the resolution of the domain name $\textsf{www.gate.org.in}$ by a $\text{DNS}$ resolver. Assume that no resource records are cached anywhere across the $\text{DNS}$ servers and that iterative query mechanism is used in the resolution. The number of $\text{DNS}$ query-response pairs involved in completely resolving the domain name is ________________.
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2 Answers

6 votes
6 votes

Answer 4.

In iterative query mechanism (left diagram), there are total 4 pairs of queries used

3 iterative quires + 1 recursive query

 

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5 Comments

Hii @Sachin Mittal 1   @Kanwae Kan Sir,

Self Doubt:

If we have one more sub-domain like www.cse.gate.org. then how many number of DNS query-response pairs involved in completely resolving the domain name ??

 

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Is this correct??

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@Sachin Mittal 1 sir , why is it not 5 , pc/client machine will make DNS query to local DNS server, why is it not counted?

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As it is – www.gate.org.in the why isn’t .org and .in counted as seperate levels/ top level servers ? Couls someone pls help.

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4 votes
4 votes

Number of query-response pairs = 4.

The name of the url is www.gate.org.in and not www.gate.in.

If it was www.gate.in , then there would have been 3 pairs because of 3 levels, namely, root DNS server, TLD server for .in and Authoritative server.

But given URL is www.gate.org.in and so there will be 4 pairs because of 4 levels, namely, root DNS server, TLD server for .in, TLD server for .org and the authoritative server.

It should be noted that the iterative query can have more than 3 levels and it is not necessary that whatever be the URL, number of levels have to be exactly 3. It can be more than that.

 

Answer:

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