To enable VPN tunnels between individual host computers or entire networks that have a firewall between them, you must open the following ports:
•To allow PPTP tunnel maintenance traffic, open TCP 1723.
•To allow PPTP tunneled data to pass through router, open Protocol ID 47.
L2TP over IPSec
•To allow Internet Key Exchange (IKE), open UDP 500.
•To allow IPSec Network Address Translation (NAT-T) open UDP 5500.
•To allow L2TP traffic, open UDP 1701.