Tag Archives: Port forwarding

Double NAT to allow IPSEC VPN on firewall behind router or firewall

On your Site 1 internet router/firewall, NAT the following ports to your VPN firewall’s External IP address


Note: To setup a proper IPSEC VPN on a firewall that is behind an internet facing router/firewall, your IPSEC VPN firewall must be assigned an internal IP address. The above example shows the IPSEC VPN firewall as

This is the IP subnet that is hosted by the internet router/firewall. is what the External interface of the IPSEC VPN firewall is assigned. Its internal subnet must be on a different subnet. This example will use

The IPSEC VPN tunnel configuration is exactly identical as if the device was the internet facing device.

In the VPN tunnel configuration, setup your local gateway to what the internet facing device (External) IP address is assigned.

On the remote IPSEC VPN tunnel, configure its remote IP address to the same IP address that is assigned to the above local gateway.


Site 1 (Home)                                                   Site 2 (Business)

Local GW:                                             Local GW:
Remote GW:                                      Remote GW:
Internal:                                Internal:
Remote:                                Remote:



Port Forwarding to Host on ASA

To forward a port to a device behind the firewall on your inside subnet, follow the steps below:

Using the ASDM, Add Network Object under the Configuration/Firewall/Objects/Network Objects/Groups settings.

Provide a Name, select Host and enter it’s IP Address.
Check the Add Automatic Address Translation Rules box.
Ensure the Type is Static.
Set the Translated Addr to outside.
Click on the Advanced… button.
Set the Source Interface to inside and the Destination Interface to outside.
Select the correct Protocol Service, then enter the correct Real Port and Mapped Port.
Click OK.


Add Access Rule under Configuration/Firewall/Access Rules.
Set the Interface to inside.
Set Action to Permit.
Set Source to any
Set Destination to the device you are forwarding the port to.
Set the Service to the Protocol/Port you are forwarding.
Click OK.port2