Figure 13-2 shows four
steps, which can be explained as follows:
|
1. |
Hannah wants to connect to web server http://www.example.com,
so she opens a browser, types in the name, and presses Enter.
|
|
2. |
Hannah's PC sends a DNS resolution request to her DNS server.
A DNS resolution request is simply a
DNS message that lists the host name (www.example.com), and the fact that the
requesting host would like to know the IP address that corresponds to that
name. |
|
3. |
The DNS sends a DNS reply back to Hannah. The DNS reply has
information in it, such as the IP address of 150.1.3.3.
|
|
4. |
Hannah can now send a packet to the web server. In fact, from
this point onward, Hannah works just like she did back in Figure 13-1, when she used a local host
file. |
For DNS to work well inside a company, someone must be
responsible for supporting it. That work includes updating and changing the list
of names and IP addresses. When new names are added, old ones are no longer
used, and when TCP/IP hosts change their IP addresses, that person has to keep
the DNS server updated.
|
 |
Although the examples in this book use web browsers, any TCP/IP
application that uses names can, and probably does, use DNS. For instance, if
you send an e-mail to barney@example.com, the "example.com" part identifies the
host name of the SMTP server that is used for example.com. | |
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