I used to use WSUS to update the machines on my home network but after a botched server upgrade, it all went screwy and I didn’t really want to have to pull all the updates down over my ADSL connection again (would probably blow away my month’s worth of “fair usage”). In any case all I was doing was blindly approving updates for installation so I might as well use the Microsoft Update servers instead.

The only downside of using the Microsoft Update servers to update several computers is that there is a lot of duplication in the network traffic. That’s why ISA Server 2006 includes a cache rule that enables caching of Microsoft updates using the Background Intelligent Transfer Service (BITS). For those who aren’t aware, BITS allows the transfer of large volumes of data without degrading network performance as it transfers the data in small chunks to utilise unused bandwidth as it becomes available and reassembles the data at the destination. The BITS feature is not available for any other ISA cache rule but the Microsoft Update Cache Rule is installed by default and all I needed to do was enable caching.

After setting up the cache rules and updating one of my servers, I wanted to see that the cache was being used. I’ve previously mentioned the cachedir.exe tool that can be used to examine ISA Server caches and I downloaded the latest version from Microsoft’s ISA Server 2006 tools page. After extracting the tool, I ran it and was presented with an error:

CACHEDIR.exe – Unable to Locate Component
This application has failed to start because msfpc.DLL was not found. Re-installing the application may fix the problem.

Then I remembered that cachedir.exe needs to be copied to the ISA Server installation folder (on my system that is %programfiles%\Microsoft ISA Server) – after moving the file to the correct folder, it fired up as expected. Just remember that this utility can only display the cache contents that have been written to disk. To flush the memory cache to disk you will need to restart the Microsoft Firewall service and re-run cachedir.exe to view the contents.