Short for Secure Socket Tunneling Protocol, SSTP is a type of VPN (virtual private network) tunnel that utilizes an SSL (secure sockets layer) 3.0 channel to send PPP (point-to-point protocol) or L2TP traffic. SSL allows transmission and data encryption and traffic integrity checking. Due to this, SSTP can pass through most firewalls and proxy servers using the SSL channel over TCP (transmission control protocol) port 443.
SSTP is available in a Windows environment (since Windows Vista SP1), in RouterOS, and SEIL (since firmware version 3.50). SSTP can be used with Winlogon or smart card authentication, remote access policies, and the Windows VPN client because of being integrated with the RRAS (routing and remote access service) architecture. As with other IP-over-TCP tunneling protocols, SSTP only performs well if there is sufficient bandwidth on the network link that is not tunneled. If enough bandwidth is not available, the tunneled TCP timers will possibly expire, causing a large decrease in SSTP performance.