Splashtop remote connections can be local (peer to peer) or remote through Splashtop relay servers. Local connections, by default, use port TCP 6783.
Local connections are enabled by default. To disable local connections, please open up the Splashtop Streamer and go to the Advanced tab. Then underneath the Local network settings, you will see an option for "Enable direct connection". Uncheck this option to disable local connections.
Splashtop detects if both devices are local or not and will automatically attempt a local connection if available. This will save on internet bandwidth usage and provide you better performance as communications are all local. However, for PCI compliance, you may want to disable the local connection option. Local connections use a self-signed cert for encryption.
Requires streamer v3.3.2.0 or later:
Note: Whether the connection is local or over relay, internet access is required to authenticate your account credentials.