Sub Domains

[S Glad]

On 17 May 2000 16:09:03 -0700, Barry Margolin <barmar at genuity.net>
wrote:

>In article <8fv7l0$k3i$1 at newssvr03-int.news.prodigy.com>,
>IcEMaN <iceman__01 at hotmail.com> wrote:
>>Hey everyone.
>>
>>I was wondering if anyone knows how to set up a subdomain to point to a
>>subdirectory of a server.  If say I have a domain xyz.com who's server is
>>111.111.111.111 and want sub.xyz.com to point to 111.111.111.111/sub/, how
>>would I do that?  Is it even possible?
>
>In DNS, make sub.xyz.com an alias:
>
>sub.xyz.com. CNAME xyz.com.

I follow you to this point
>
>Then configure the virtual hosts in your web server the same way you would
>if they were two unrelated domains.

I don't understand this part. With a normal domain the INDEX.HTML file
is the "startup file" for the web page. How do you define what the
"startup file"  is for the sub domain?