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Server Name Indication(SNI) is an extension of Transport Layer Security which allows multiple secure web sites, with separate certificates, to be hosted at the same IP address

Server Name Indication addresses a common issue where websites with an SSL certificate had to live on separate IPs. This exacerbated the IPv4 shortage, as well as defeated the purpose of virtual hosting, where multiple non-secured sites could share the same IP (note that websites sharing a common certificate can always share an IP).

SNI is based on IETF RFC 4366, which, as part of Transport Layer Security(TLS), allowed the hostname to be sent in the initial stages of the TLS handshake. This allowed websites with different certificates to be hosted on the same IP.

SNI is supported by all major browsers and all major web servers. It requires OpenSSL 0.9.8f or later

Browser Support

  • Mozilla Firefox 2.0 or later
  • Opera 8.0 or later (with TLS 1.1 enabled)
  • Internet Explorer 7.0 or later (on Vista, not XP)
  • Google Chrome
  • Safari 3.2.1 on Mac OS X 10.5.6

Server Support

  • Apache v2.2.12 or later
  • Nginx 0.5.32 or later
  • IIS 8.0 or later
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