Why is it not possible to use Name-Based Virtual Hosting to identify different SSL virtual hosts?
Name-Based Virtual Hosting is a very popular method of identifying different virtual hosts. It allows you to use the same IP address and the same port number for many different sites. When people move on to SSL, it seems natural to assume that the same method can be used to have lots of different SSL virtual hosts on the same server.
The reason is that the SSL protocol is a separate layer which encapsulates the HTTP protocol. So the problem is that the SSL session is a separate transaction that takes place before the HTTP session even starts. Therefore all the server receives is an SSL request on IP address X and port Y (usually 443). Since the SSL request does not contain any Host: field, the server has no way to decide which SSL virtual host to use. Usually, it will just use the first one it finds that matches the port and IP address.
You can, of course, use Name-Based Virtual Hosting to identify many non-SSL virtual hosts (all on port 80, for example) and then you can have no more than 1 SSL virtual host (on port 443). But if you do this, you must make sure to put the non-SSL port number on the NameVirtualHost directive, e.g.
Other workaround solutions are:
Use separate IP addresses for different SSL hosts. Use different port numbers for different SSL hosts.
Specifically, you cannot have multiple secure virtual hosts on the same SOCKET (IP address + port). By default, a secure host will use port 443. You can change configure your virtual host to use a different port number with the same IP, thus creating another socket. There are many disadvantages to this approach. The most obvious disadvantage is that if you are not using the default port, your URL must also contain the port number to access the secure site.
Site using default port - www.something.com - would be accessed as https://www.something.com
A site using port 8888 would be accessed as https://www.something.com:8888
Another disadvantage is that if you introduce more ports, you will be providing more opportunities for port sniffing hackers. Last, if you select a port that is used by something else, you will create conflict problem.