What ports do I need to open to permit VPN traffic ?
For PPTP VPN connections, you need to open TCP port 1723 (for PPTP tunnel maintenance traffic). PPTP also uses IP protocol 47 for tunneling data (for "General Routing Encapsulation" or GRE packets).
For L2TP/IPSEC VPN connections, you need to open UDP port 500 for Internet Key Exchange (IKE) traffic, UDP port 4500 (IPsec control path) and UDP port 1701 for L2TP traffic. IPsec ESP traffic also uses IP protocol 50.
SSTP connections use TCP port 443 (SSTP traffic to/from the VPN server)