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Now consider an interesting case of a corporate computer that needs to resolve an
external name of a computer from its own company.
A computer in the YYY Corporation needs to open a web page on the
www.yyy.com. machine. Since it is a proxy client it sends a request to the proxy
server (Step 1) after it finds that the name www.yyy.com. is external, based on the
PAC file. The proxy server sends a DNS query to the assigned DNS server (Step 2)
which happens to be authoritative for www.yyy.com. The DNS server resolves the
query and returns the response to the proxy client (Step 3). Finally the proxy server
uses the obtained IP address of www.yyy.com. to contact it and provides necessary
info to the client (Step 4).
Windows 2000 White Paper
53
External world / Global Network
YYY corporation
ZZZ corporation
YYY corporation
ZZZ corporation
VPN
VPN
Proxy Server
Firewall
A
DNS Server, Firewall, VPN or Proxy Server
A
DNS Client
first.yyy.com. second.yyy.com. third.yyy.com. third.zzz.com.first.zzz.com.
second.zzz.com.
. zzz.com.
yyy.com.
yyy.com.
yyy.com. zzz.com.
someother.com.
com.
.
1
2
1
2
Zone.Name.
Primary Zone Secondary Zone
Zone.Name.
3
3
4
4