Point-to-Point Tunneling Protocol (PPTP) ALGs

The Point-to-Point Tunneling Protocol (PPTP) ALG is a TCP-based ALG. PPTP allows the Point-to-Point Protocol (PPP) to be tunneled through an IP network. PPTP defines a client-server architecture, a PPTP Network Server, and a PPTP Access Concentrator. The PPTP ALG requires a control connection and a data tunnel. The control connection uses TCP to establish and disconnect PPP sessions, and runs on port 1723. The data tunnel carries PPP traffic in generic routing encapsulated (GRE) packets that are carried over IP.