I had the same issue. I have the solution, but let's outline the problem more thoroughly, first.
I want to take advantage of SNI support in ISPConfig > 3.0.4, but when I (re)start Apache, I see the following:
The relevant Apache documentation ( http://wiki.apache.org/httpd/NameBasedSSLVHostsWithSNI ) states:
# service apache2 restart
* Restarting web server apache2
[Thu Dec 15 09:03:32 2011] [warn] _default_ VirtualHost overlap on port 443, the first has precedence
[Thu Dec 15 09:03:33 2011] [warn] _default_ VirtualHost overlap on port 443, the first has precedence
My software supports SNI as evidenced by the following message in my error log upon Apache startup:
How can you tell if your Apache build supports SNI? ... If SNI is built in, then the error log will show "[warn] Init: Name-based SSL virtual hosts only work for clients with TLS server name indication support (RFC 4366).
Further, if I examine the Apache environment variables (e.g. via PHP's phpinfo() function), I see:
[Thu Dec 15 09:03:33 2011] [warn] Init: Name-based SSL virtual hosts only work for clients with TLS server name indication support (RFC 4366)
So, Apache and my browser are SNI-enabled.
And now for the solution:
As always, "the devil is in the details".
The only part you missed was adding this to your Apache configuration, e.g., at the top of /etc/apache2/httpd.conf
(this is from the same document that is referenced above):
# Listen for virtual host requests on all IP addresses
Don't forget to restart Apache (a reload probably works just as well).