My site with the main domain name www.mysite.com works well before. (I use mysite to hide my actual domain name here)
I want to add sub.mysite.com for another virtual host on my host.
I follow http://davidpodley.com/2010/02/11/setti ... nd-apache/ and after I do
a2ensite sub.mysite.com
/etc/init.d/apache2 restart

some users of www.mysite.com will access sub.mysite.com not www.mysite.com. I can found them in /srv/www/sub.mysite.com/logs/access.log and they tell me the problem. They should only access www.mysite.com. However, it works well on my PC.

Why the users of www.mysite.com go to sub.mysite.com? Can anyone help me?
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Some informations:

My A Records is:
Hostname IP Address TTL Options
96.126.98.96 Default Edit | Remove
sub 96.126.98.96 Default Edit | Remove
mail 96.126.98.96 Default Edit | Remove
www 96.126.98.96 Default Edit | Remove

my hostname is mysite, and my /etc/hosts is
127.0.0.1 localhost.localdomain localhost
96.126.98.96 mysite.mysite.com mysite

apache2ctl -S:
VirtualHost configuration:
wildcard NameVirtualHosts and _default_ servers:
*:443 is a NameVirtualHost
default server mysite.com (/etc/apache2/sites-enabled/mysite.com:10)
port 443 namevhost mysite.com (/etc/apache2/sites-enabled/mysite.com:10)
*:80 is a NameVirtualHost
default server sub.mysite.com (/etc/apache2/sites-enabled/sub.mysite.com:1)
port 80 namevhost sub.mysite.com (/etc/apache2/sites-enabled/sub.mysite.com:1)
port 80 namevhost mysite.com (/etc/apache2/sites-enabled/mysite.com:1)

cat /etc/apache2/sites-enabled/mysite.com
<VirtualHost *:80>
ServerAdmin mysite@gmail.com
ServerName mysite.com
ServerAlias www.mysite.com
DocumentRoot /srv/www/mysite.com/public_html/
ErrorLog /srv/www/mysite.com/logs/error.log
CustomLog /srv/www/mysite.com/logs/access.log combined
</VirtualHost>

<VirtualHost *:443>
SSLEngine On
SSLCertificateFile /etc/apache2/ssl/apache.pem
SSLCertificateKeyFile /etc/apache2/ssl/apache.key

ServerAdmin mysite@gmail.com
ServerName mysite.com
ServerAlias www.mysite.com
DocumentRoot /srv/www/mysite.com/public_html/
ErrorLog /srv/www/mysite.com/logs/error.log
CustomLog /srv/www/mysite.com/logs/access.log combined
</VirtualHost>

cat /etc/apache2/sites-enabled/sub.mysite.com
<VirtualHost *:80>
ServerAdmin mysite@gmail.com
ServerName sub.mysite.com
ServerAlias www.sub.mysite.com
DocumentRoot /srv/www/sub.mysite.com/public_html/
# DocumentRoot /srv/www/mysite.com/public_html/sub
ErrorLog /srv/www/sub.mysite.com/logs/error.log
CustomLog /srv/www/sub.mysite.com/logs/access.log combined
</VirtualHost>

It's resolved.
Some users access my main domain site with IP directly.
In apache2ctl -S result, we can see

default server sub.mysite.com

According apache explanation, the first <VirtualHost *:80> in the configuration file has the highest priority and can be seen as the default or primary server.
In my server, /etc/apache2/sites-enabled, rename mysite.com to 000mysite.com will make it be loaded before sub.mysite.com (in my site, "sub" is "f*")