PPTP traffic uses TCP port 1723, and IP protocol uses ID 47, as assigned by the Internet Assigned Numbers Authority (IANA). PPTP can be used with most firewalls and routers by enabling traffic destined for TCP port 1723 and protocol 47 to be routed through the firewall or router.
Firewalls ensure corporate network security by strictly regulating data that comes into the private network from the Internet. An organization can deploy a PPTP server running Windows NT Server version 4.0 behind its firewall. The PPTP server accepts PPTP packets passed to the private network from the firewall and extracts the PPP packet from the IP datagram, decrypts the packet, and forwards the packet to the computer on the private network.