Packet filtering

Although the primary purpose of IPSec is to ensure the integrity of hosts and to encrypt traffic, the Windows Server 2003 IPSec implementation also provides limited firewall capabilities for end systems. This was extremely important with versions of Windows released prior to Windows XP. However, Windows XP and Windows Server 2003 include Internet Connection Firewall (ICF), which provides more powerful stateful packet filtering than IPSec.

Although IPSec and ICF functionality overlap, they both have unique features. ICF is stateful, and IPSec provides filtering based on source and destination IP addresses. Fortunately, there's nothing to stop you from using both together on computers running Windows XP Professional and Windows Server 2003.

See Also For more information about ICF and stateful packet filtering, refer to Chapter 4.

You should enable ICF on computers running Windows XP Professional and Windows Server 2003 regardless of whether you use IPSec. However, to ensure proper IKE management of IPSec SAs, you must configure ICF to permit ISAKMP for UDP port 500. If you are using NAT-T, you must also allow traffic on UDP port 4500. ISAKMP is not one of ICF's pre-configured services, however, so you will need to add it. To add ISAKMP, click the Advanced tab in the filtered network interface's properties dialog box. Then click the Settings button. Click the Services tab, and then click Add. Enter settings in the dialog box as shown in Figure 8.5, and then click OK and repeat the process for the second port number.

Description of service: [ISAKMP

Name or IP address (for example] of the computer hosting this service on your network: |

External Port number for this service:

Internal Port number for this service:


Figure 8.5 Allowing the ISAKMP service through ICF

Lesson 3 provides information on configuring packet filtering by using IPSec.

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