Off the Record There's one way to use multiple security policies on a single computer: by using virtual machines. I use virtual machines extensively to run multiple instances of different operating systems on a single computer simultaneously. Enterprises often use virtual machines in servers to avoid conflicts between server applications, such as the limitation of having a single IPSec policy applied to a computer. I use Microsoft Virtual PC 2004. You can find information about this software at

When designing IPSec policies for your organization, follow one guideline before all others: keep it simple. Although you might want to provide different levels of security for different computers, use as few policies as possible to minimize the complexity of your system. A simpler system is less likely to produce problems and is also easier to troubleshoot if it does. You can further simplify the process of deploying IPSec by using the built-in policies: Client, Request Security, and Require Security. These policies have been configured to provide the maximum level of compatibility possible without significantly sacrificing security.

There is a significant limitation to using IPSec to protect communications within a domain: you should not use IPSec and Kerberos authentication between domain members and domain controllers. Establishing an IPSec connection requires sending a request to a domain controller, but if that request requires an IPSec connection to be established, you will never be able to complete the Internet Key Exchange (IKE) negotiation. In addition, no other authenticated connections can be made using other protocols, and no other IPSec policy settings can be applied to that domain member through Group Policy. For these reasons, Microsoft does not support using IPSec for communications between domain members and domain controllers.

There are additional limitations when using IPSec to protect traffic to a cluster. Many clustering and load-balancing services use the same IP address for all nodes in a cluster, which creates incompatibilities with IPSec. Windows Server 2003 IPSec has proprietary extensions that allow it to work with the Windows Server 2003 Network Load Balancing service and Windows Cluster Service. However, support for these extensions does not exist in the current Microsoft Windows 2000 and Windows XP IPSec client implementations, so you will experience some loss of connectivity when you add or remove Windows 2000 cluster nodes.

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