DZone

When you have multiple websites and want to run them on one IP address, you use name-based virtual hosting. Using a name-based host, you can quickly direct a user to the right site. However, this becomes a problem while using SSL/TLS certificates. That’s because SSL/TLS involves a handshake between the client and server. An HTTP header can only be sent after the handshake. As a result, the server doesn’t know which website it should serve. That’s why it forces some people to purchase separate IP addresses.

Here Comes SNI 

Server Name Indication (SNI) is an extension to the SSL/TLS protocol. It allows you to host multiple SSL certificates on a single unique IP address. This is done by inserting an HTTP header in the SSL/TLS handshake. This saves some serious money.

Source: DZone