VPN port number

quoted from http://www.howtonetworking.com

Which ports need to be opened for running VPN

PPTP VPN uses TCP Port 1723,

IP Protocol 47 (GRE);

L2TP: UDP Port 1701;

IPSec: UDP Port 500,

Pass IP protocol 50 and 51.

Note: 47 is a protocol number and not TCP port. The protocol name is GRE. It'll make a big difference when configuring your firewall or router.