Apache Virtual Hosts with a Wildcard DNS Record

Question

Here is my current setup:

At the bottom of httpd.conf I have the following:

NameVirtualHost *:80
Include /etc/httpd/conf/vhosts/*

Inside of /etc/httpd/conf/vhosts I have the following files:

mainsite.com.conf:

<VirtualHost *:80>
  DocumentRoot "/var/www/vhosts/mainsite.com"
  ServerName mainsite.com
  ServerAlias www.mainsite.com
  <Directory "/var/www/vhosts/mainsite.com">
    allow from all
    Options -Indexes
  </Directory>
</VirtualHost>

sub1.mainsite.com.conf:

<VirtualHost *:80>
  DocumentRoot /var/www/vhosts/sub1.mainsite.com
  ServerName sub1.mainsite.com
  <Directory "/var/www/vhosts/sub1.mainsite.com">
    allow from all
    Options -Indexes
  </Directory>
</VirtualHost>

So far so good! mainsite.com and www.mainsite.com both share the same DocumentRoot (and with some redirection later I can redirect all www.mainsite.com users to mainsite.com for SEO). sub1.mainsite.com also has its own DocumentRoot and doesn't interfere with anything else.

However, <Anything that isn't www or sub1>.mainsite.com gets the same DocumentRoot that mainsite.com and www.mainsite.com get. What I would prefer instead is an error page to come up for any host that doesn't match a VirtualHost.

And now for the actual question: What can I tweak to get the desired effect? Also, can the directory rules that are common between the VirtualHosts be refactored up into httpd.conf? If so, would I just do something like the following?

<Directory "/var/www/vhosts">
  allow from all
  Options -Indexes
</Directory>

Answer 1

<VirtualHost *:80>
ServerAlias *.mainsite.com
...
... 
</VirtualHost>

Should catch anything that isn't otherwise defined.

Answer 2

I use a catchall vhost definition that is the last to be read

<VirtualHost *:80>
        ServerName      default
        ServerAlias *
        DocumentRoot /var/www/default
        ErrorDocument 404 /404.html
        <Directory "/var/www/default">
            Options All
            AllowOverride None
            allow from All
        </Directory>
</VirtualHost>

The default index.html file tells the user that there is noting to see at the address supplied. The 404.html file same.