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Home > Archive > 70-216 > December 2001 > DNS Queries
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| mrbeej 2001-12-06, 7:47 pm |
| Perhaps someone can shed some light on this for me. In the Sybex Study Guide, Chapter2 Windows Naming Services, page 54, is an example of recursive and iterative queries. Now the client or resolver is making a recursive query, and the Name Server is performing a bunch of Iterative queries, in order to get to the answer.
On the 070-216 CBT Nugget for DNS, Dan talks about a similar scenario, however he states that the client is making an Iterative query and the Name Server is making the recursive queries. It seems to be the same scenario but a completely opposite interpretation to the one in the Sybex book. Perhaps I am understanding this incorrectly, but what is the right answer for this one.
Thanks in advance
MrBeej | |
| wbafrank 2001-12-06, 9:55 pm |
|  I have just looked up this in my MS Training Kit and have found the following:
Recursive Queries - In a recursive query, the queried name server is petitioned to respond with requested data, or with an error stating that data of the requested type does not exist or that the domain name specified does not exist. The name server cannot refer the request to a different name server.
Iterative Queries - In an iterative query, the queried name server gives the best answer it currently has back to the requester. This answer may be the resolved name or a referral to another name server that may be able to answer the client's original request.
They then give an example of both recursive and iterative queries as follows:
A client within a corporation is querying its DNS server for the IP address for www.mycomputer.com.
This what happens:
a. The resolver sends a recursive DNS query to its local DNS server asking for the IP address of www.mycomputer.com. The local name server is responsible for resolving the name and cannot refer the resolver to another name server.
b. The local name server checks its zones and finds no zones correspoding to the requested domain name. It then sends an iterative query for www.mycomputer.com to a root name server.
c. The root name server has authority for the root domain and will reply with the IP address of a name server for the com top-level domain.
d. The local name server sends an iterative query for www.mycomputer.com to the com name server.
e. The com name server replies with the IP address of the name server servicing the www.mycomputer.com domain.
f. The local name server sends an iterative query for www.mycomputer.com to the mycomputer.com name server.
g. The mycomputer.com name server replies with the IP address corresponding to www.mycomputer.com.
h. The local name server sends the IP address of www.mycomputer.com back to the original resolver.
 Sorry to waffle, but I hope this clears up your query! |
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