Shiva Smart Tunneling, also referred to as SST is a simplistic UDP-based VPN tunneling protocol developed by Shiva Corp. (whose assets are now owned by Eicon) for its Shiva series VPN gateways. Shiva Smart Tunneling works on UDP port 2233 by default, but can be configured to use IP protocol number 99 (reserved by IANA as 'any private encryption scheme').
