SNI

Abbreviation · Development

Definitions

  1. Server Name Indication -- a TLS extension that lets the client specify which hostname it's connecting to during the handshake, before encryption begins. Enables hosting multiple HTTPS sites on a single IP address (each with its own certificate). Without SNI, each HTTPS site required a dedicated IP. Supported by all modern browsers since ~2010.

    In plain English: A TLS feature that tells the server which website you want during the handshake, enabling multiple HTTPS sites on one IP address.

    Example: "SNI lets nginx serve different certificates for site-a.com and site-b.com on the same IP -- the client sends the hostname in the ClientHello."

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