muha med thinks this is interesting: The Point-to-Point Tunneling Protocol (PPTP) uses GRE, so if you’re using this protocol for VPN access, you will need to allow GRE on your firewall. From GRE and Access Lists from Network Warrior, 2nd Edition by Gary A. Donahue Publisher: O'Reilly Media, Inc. Released: May 2011 Note What needs to be enabled on Firewall to enable GRE Share this highlight http://www.safaribooksonline.com/a/network-warrior-2nd/16603/ Twitter Facebook Google Plus Email Get Instant Access Now Start a Free Trial Have an account? Sign in. Minimise Unlock the rest of Network Warrior, 2nd Edition and 30,000 other books and videos By clicking this box, you confirm that you have read and agree to the terms and conditions of our Membership Agreement, and you understand that when your trial period ends, you will be required to provide billing information if you wish to continue using the service. Unlock the rest of this book Start a Free 10-Day Trial loading Learn about Safari for Business Have an account? Sign in.