firewalls and vpn

TCP and UDP Ports, IP ports

which once used port 47 and protocol number 1723 and configuration

using VPN and PPTP for connectivity thru a firewall. The scenario shows

picture of Two fire walls and Two VPN servers,each of the VPN servers is

behind the firewall, located at Boston and NY respectively and connected

together thru the internet. You try to connect using one of the VPN servers.

You get the error “can’t connect”. What to do on the firewall walls to allow

the VPN servers to communicate. I have no idea.