Server Name Indication (SNI) is an extension to Transport Layer Security (TLS) where a client indicates which hostname it is attempting to connect to at the start of the handshaking process. The extension allows a server to present one of multiple possible certificates on the same IP address and port number, allowing for multiple services to be served by the same IP address without using a single certificate. For HTTPS, it is the conceptual equivalent to HTTP/1.1 virtual hosting. In the original specification, the hostname is not encrypted; the later Encrypted Client Hello specification rectifies this. The SNI extension was specified in 2003 in RFC 3546.