MCSA/MCSE Self-Paced Training Kit (Exam 70-270): Installing ...

13-34 Chapter 13 Supporting TCP/IP
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Local
2
name server Root
name server
1
Client
Figure 13-10 A forward lookup query resolves a name to an IP address.
The numbers in Figure 13-10 depict the following activities:
1. The client passes a forward lookup query for www.microsoft.com to its local name
server.
2. The local name server checks its zone database file to determine whether it contains
the name-to-IP address mapping for the client query. The local name server
does not have authority for the microsoft.com domain, so it passes the query to
one of the DNS root servers, requesting resolution of the host name. The root
name server sends back a referral to the com name server.
3. The local name server sends a request to a com name server, which responds with
a referral to the Microsoft name server.
4. The local name server sends a request to the Microsoft name server. Because the
Microsoft name server has authority for that portion of the domain namespace,
when it receives the request, it returns the IP address for www.microsoft.com to
the local name server.
5. The local name server sends the IP address for www.microsoft.com to the client.
6. The name resolution is complete, and the client can access www.microsoft.com.
What Is Name Server Caching?
5
6
4
3
The Web
Microsoft
name server
Com
name server
When a name server is processing a query, it might be required to send out several
queries to find the answer. With each query, the name server discovers other name
servers that have authority for a portion of the domain namespace. The name server
caches these query results to reduce network traffic.