Implementing an IPSEC Site to Site VPN between ISA Server 2006 Beta and Cisco PIX 501

ISA Server 2006 is the next step in Microsoft’s Security Strategy. ISA Server 2006 is the successor of ISA Server 2004. ISA Server 2006 RTM is expected to be released at the end of June 2006 so this article is based on a Beta version of ISA Server 2006.

For you to better understand, I created a Topology diagram about the ISA Server 2006 and Cisco Pix config.


We are starting the Site to Site VPN configuration at ISA Server 2006 site. Start the ISA Server Management console and navigate to Virtual Private Networks (VPN) to create a new VPN Site to Site Network.



Name the new Site to Site VPN network PIXNET.


Cisco Pix only supports IP Security (IPSEC Tunnel Mode), so we select this option. For every other Site to Site VPN you shouldn’t select IPSEC Tunnel Mode VPN.


Specifiy the IP address of the Outside interface from Cisco Pix and the Local Interface IP address from ISA Server 2006.


For a Site to Site VPN Gateway connection you must use a certificate from a CA or a Pre Shared Key. For this example we will use the very simple Pre Shared Key 12345678. If you don’t use certificates, which is recommended, you should specify a long and complex Pre Shared Key.


Now specify the Remote Site network behind the Cisco Pix which you want to access from ISA Server site.


Read the summary of the Wizard and finish the VPN configuration on ISA site.


View the IPSEC Policy configured by the ISA Site to Site VPN wizard.


Take note of the IPSEC Policy settings because they must match the Settings that you will configure on Cisco PIX site.


After creating the Site to Site VPN you must create a Network rule between Cisco Pix and ISA.


The Source Network is Internal.


The Network destination is the Cisco Pix Network PIXNET.


The Network Relationship is Route.


After creating the Network Rule you must create two Firewall rules to allow access between Cisco PIX Net and ISA Net. If the two networks are trusted, create a Firewall rule which allows full access or else create a Firewall rule with limited access.


Now it is time to configure the Cisco Pix site. Start the Cisco PDM.


Start the Cisco Pix VPN Wizard and select Site to Site VPN. The Interface is the Outside Interface.


Specify the Peer IP Address. This is the IP Address of the external ISA Server 2006 interface.

Enter the Pre Shared Key that you had configured at ISA Server Site (12345678).



Enter the IKE Policy settings shown in the following picture to match the ISA VPN config.


Next, specify the Transform Set settings shown in the following picture.


In the next VPN Wizard dialog page enter the IP Address Range from the Network behind the Pix (from the Inside Interface).


Enter the IP address range from the Internal network protected by ISA Server 2006.


If it is the First time that PDM creates the Network, PDM asks to add the Remote Host or Network to the Cisco Pix configuration set. Click OK.


Enter the configuration information for the remote Site network. Select the Outside Interface of the Pix.


Cisco Pix must know the route to the Remote Site Network so create a static route to the Destination Network.


Click Finish to close the Network Create Wizard at Cisco Pix Site.


Click Finish.


Click Save to store the VPN configuration in Cisco Pix NVRAM.


After creating the VPN Site to Site configuration at Cisco Pix site, you must change some IPSEC settings. To do so, click Access Rules and then IPSEC – Tunnel Policy.


In the following picture you can see the Cisco Pix config settings for the Tunnel Policy before modifying.


You must change the Security Association Lifetime to 100000 Kilobytes, the Lifetime to 01 Hour and enable PFS (Perfect Forward Secrecy).


After changing IPSEC Policy settings click IKE – Policies and then Edit.


IKE Policy before changes


Change the IKE Lifetime from 86400 seconds to 28800 seconds.



The last step is to configure the same IKE and ISPEC Policy settings made in the Cisco PIX config also on ISA Server site. Start the ISA Management Console and click into the Properties of the Site to Site VPN connection to the Cisco Pix and click Connection – IPSEC Settings – Phase II and change the Key generation to every 100000 Kbytes.