What is Server Name Indication (SNI)?

Last updated on 28 Sep 2023, 10:22:54.
Category: All about SSL certificates

Apache Nginx SNI

What is SNI?

Server Name Indication is a recent extension of the TLS and SSL protocol that allows a browser to indicate at the beginning of the SSL connection which hostname the browser is connecting to. The main advantage of SNI is that it allows multiple SSL certificates to be associated with the same IP address of a web server, rather than having to provide a separate IP address for each SSL website.

How does SNI work?

The HTTP protocol has supported the concept of name-based virtual hosting since version 1.1. At the beginning of the connection to the web server, the browser specifies the hostname it wants to connect to, and this hostname is read from the host headers provided in the browser request. With an SSL connection, this is not possible by default, because the handshake of the SSL connection takes place before the browser request is decrypted and the web server can figure out which hostname is being requested.
Websites hosted on the same IP address must necessarily use the same SSL certificate, or have their own IP address, which is not appropriate with the current scarcity of IPv4 addresses.

So SNI solves this problem. SNI is an extension of the TLS protocol where the hostname is sent as "part" of the SSL/TLS handshake.
This allows the Web server to select the correct Web site and present the correct certificate to the browser.

Related articles

Order an SSL certificate? What is an SSL certificate?

You need to order an SSL certificate? But what is an SSL certificate? And why is everyone saying that it...

Read more

SHA1, SHA2 and SHA256 SSL algorithms

SHA is a mathematical algorithm used in SSL encryption to verify the validity of the certificate's signature. Different iterations of...

Read more

Why do I see a yellow warning triangle on an HTTPS secured website?

The yellow warning triangle you may see when visiting a webpage that's secured with SSL, is an indication that Google...

Read more

Need extra help?

Were not all your questions answered?
Don't worry, we will be happy to help you via a support request!

Select your language

All languages: