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How to pass PPTP traffic through a PIX Firewall

Cisco PIX Firewalls require two elements to pass traffic from outside (higher security) to inside (lower security): a static translation and a conduit.

For this example, assume a server has IP address 192.168.1.100 and there is an available outside address of 1.1.1.1.

First, create the static translation. This configuration line establishes a relationship between 1.1.1.1 (public Internet IP address) and 192.168.1.100 (inside, private IP address).


static (inside,outside) 1.1.1.1 192.168.1.100 netmask 255.255.255.255 0 0


Next, create appropriate conduits to allow specific traffic to pass from the outside to the Inside interface. PPTP uses TCP/1723, TCP/139, UDP/Netbios-NS, UDP/Netbios-DGM, and IP/47 GRE.


conduit permit tcp 1.1.1.1 eq 1723 any
conduit permit tcp host 1.1.1.1 eq 139 any
conduit permit udp host 1.1.1.1 eq 137 any
conduit permit udp host 1.1.1.1 eq 138 any
conduit permit gre host 1.1.1.1 any

or

access-list 101 permit tcp any host 1.1.1.1 1723
access-list 101 permit tcp any host 1.1.1.1 139
access-list 101 permit udp any host 1.1.1.1 137
access-list 101 permit udp any host 1.1.1.1 138
access-list 101 permit gre any host 1.1.1.1
access-group 101 in interface outside


A couple of notes:

• In the conduits and access-lists, the any keyword allows matching traffic from any IP address to pass through the firewall. This should be replaced with the source IP address of the PPTP tunnel, if at all possible.
  
  In the access-lists, verify any existing access-lists or other traffic needed before entering the last line!