Knowledge Base

SSL certificates and Server Name Indication (SNI) support

This article discusses Server Name Indication (SNI) support at A2 Hosting.

What is SNI?

Server Name Indication (SNI) is an extension to the Transport Layer Security (TLS) protocol that enables servers to use multiple SSL certificates on one IP address. In practical terms, this means:

  • As the number of available IPv4 addresses becomes smaller and smaller, the remaining addresses can be allocated more efficiently.
  • In most cases, you can run an SSL-enabled site without having to purchase a dedicated IP address. For more information, please read the following section.

Do I need to purchase a dedicated IP address for my SSL certificate?

The answer to this question depends on two things: whether your A2 Hosting server supports SNI, and whether your site visitors use web browsers that support SNI.

A2 Hosting server SNI support

The following A2 Hosting servers do not support SNI:

  • to
  • to

These servers run a version of OpenSSL that does not support SNI. Therefore, to install an SSL certificate on any of these servers, you must also purchase a dedicated IP address.

All other A2 Hosting servers support SNI, and do not require a dedicated IP address to install an SSL certificate.

For information about how to determine your account's server name, please see this article.
Browser SNI support

In addition to server SNI support, users' web browsers must support SNI. Fortunately, almost all modern operating systems and web browsers support SNI.  However, there are a few notable exceptions of browsers that do not support SNI:

  • All versions of Internet Explorer on Windows XP.
  • Safari on Windows XP.
  • BlackBerry OS 7.1 and earlier versions.
  • Windows Mobile 6.5 and earlier versions.
  • Android default browser on Android OS 2.x.

If you have a significant number of visitors that use one or more of these browsers, SNI is probably not the best choice. You should purchase a dedicated IP address and use an SSL certificate without SNI instead.

More Information

For more information about SNI, please visit