apache virtual host question

After i 've set a virtual host in httpd.conf,

why i still have to set the virtual host in domain registration organization?

I'clarify

for example , i've set phpmyadmin.mydomain.com as virtual host in httpd conf file, ne开发者_如何学运维xt, i've to go to http://www.dyndns.com/ to add phpmyadmin.mydomain.com as A record, so phpmyadmin.mydomain.com will be accessible.

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After i 've set a virtual host in httpd.conf,

why i still have to set the virtual host in domain registration organization?

These are two separate tasks because they touch entirely different areas.

DNS records tell the world that domain A is now reachable on IP address B (Imperfect real world analogy: an entry in the phone book)

The VirtualHost directive tells the server software running on the server how to deal with incoming requests to that domain. (Imperfect real world analogy: Your name on the doorbell of a large house, and on your mail box in the hallway of the house.)