Short for Secure Socket Tunneling Protocol, SSTP is a type of VPN tunnel that utilizes an SSL 3.0 channel to send PPP or L2TP traffic. SSL allows for transmission and data encryption, as well as traffic integrity checking. Due to this, SSTP can pass through most firewalls and proxy servers by using the SSL channel over TCP port 443.
SSTP is available to use in a Windows environment (since Windows Vista SP1), in RouterOS and in 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 architecture. As with other IP-over-TCP tunneling protocols, SSTP only performs well if there is sufficient bandwidth on the un-tunneled network link. If enough bandwidth is not available, the tunneled TCP timers will possibly expire, causing a large decrease in SSTP performance.