What is SNI (Server Name Indication)?

SNI (Server Name Indication) allows multiple websites with different SSL certificates to share the same server address, like having multiple businesses operate from the same building but each with their own security system. Without SNI, each SSL certificate would need its own unique server address, making hosting much more expensive and complicated.

How SNI Works

SNI extends the TLS handshake process to support multiple certificates on one server:

Client Hello Extension: Browser includes the hostname it wants to reach
Server Certificate Selection: Server chooses the appropriate certificate for that hostname
Multiple Domains: One server can host many different websites securely
Shared Resources: Reduces server costs and simplifies hosting infrastructure
Backward Compatibility: Works with modern browsers and systems

Benefits and Limitations

SNI dramatically reduces hosting costs and complexity by allowing certificate consolidation on shared servers. This is especially valuable for hosting providers and organizations managing multiple domains. However, SNI requires support from both the client and server, and very old browsers or systems may not support it. Most modern web traffic supports SNI, making it the standard approach for multi-domain SSL hosting in cloud environments and shared hosting platforms.