The Cache Array Routing Protocol (CARP) significantly enhances the basic Web caching capabilities found in Microsoft Internet Security and Acceleration Server (ISA Server) 2006 Standard Edition.

Cache Array Routing Protocol (CARP) allows you to distribute the Web proxy cache across multiple array servers. In addition, Web content is never duplicated. A Web object is placed on a single member of the CARP array and is never stored on any other array member computer. This reduces the overall amount of disk space required across "Array members".

Microsoft Internet Security and Acceleration Server (ISA Server) 2006 Enterprise Edition Web caching arrays also provide load balancing and fault tolerance. When the Web Proxy clients are configured with the auto configuration script, they are able to correctly identify which ISA Server firewall array member is responsible for Web content that they want to retrieve.

I will enable CARP to create a MS Internet Security and Acceleration Server (ISA Server) 2006 Enterprise Edition Web caching array.

Key steps are:

1. Create cache drives on the array.
2. Enable the Web Proxy listener on the intra-array network interfaces. The Web Proxy listener must be enabled on the interfaces used by each array member on the dedicated intra-array communications network.
3. Enable CARP on the array. CARP can be enabled on a per-network basis. You want internal network hosts to be able to use CARP, so you will enable CARP on the relevant "Internal network" interfaces of the array.
4. You would enable CARP on the External network in situations where the "Array Members" are also being used as "Reverse Proxy" / "Web Publishing" servers.
5. Enable automatic discovery on the "Internal network" "LAN subnet". Automatic discovery allows Web Proxy clients to use Web Proxy Automatic Discovery (WPAD) entries in DNS or Dynamic Host Configuration Protocol (DHCP) to automatically discover the array's auto configuration information.

Note: I will not go into details of how to configure WPAD right now but if I get a chance will cover this at a later date.

6. Configure Web browsers to use the auto configuration script through automatic discovery. The auto configuration script enables Web Proxy clients to determine which member of the Web caching array is responsible for the requested Web content.

Step 1 - Enable caching and configure cache settings and rules.
Step 2 - Enable CARP on the internal network.
Step 3 - Configure a CARP load factor for each array member.
Step 4 - Enable Web Proxy client requests on the intra-array communication network.

Create Cache Drives on the Array

Web caching is disabled by default on Microsoft Internet Security and Acceleration Server (ISA Server) 2006 Enterprise Edition arrays. The first step to create a distributed CARP-enabled Web caching array is to create cache drives on each array member.

Perform the following steps to create cache drives on each member of the firewall array, in this example; the array is called "EntArray".

Step 1: Open the ISA Server 2006 Enterprise Edition console, expand the array name, and then expand the Configuration node in the left pane of the console. Click the Cache node.

Step 2: Right-click the "ISA01" in the details pane and click Properties. OR on the right hand "Task Pane" select "Define Cache Drives"

Step 3: In the Array Properties dialog box, enter a value for the size of the cache file on the Array computer. In this example, I will create a 2 GB cache file. Enter 2048 in the Maximum cache size (MB) text box and click Set. Click Apply, and then click OK.
Note: Always ensure you select the appropriate partition with enough free disk space. For performance reasons if you have a dedicated mirrored drive would be ideal.

Step 4: In the details pane, right-click "ISA02" and click Properties.

Step 5: In the "ISA02" Properties dialog box, configure the same settings.



Step 6: The size of the cache files appears in the Cache Size on NTFS Drives (MB) column in the details pane.
Note: If the file cache size entered is more than 10 GB I have noticed it does take sometime to create the file and hence the console might seem unresponsive for a few seconds depending on the performance of your hardware. Remain calm & be patient and let it catch up!!! :)

Step 7: You can verify your configuration before it is saved. Once the above settings are configured, click "Cache Drives" as indicated below.



Step 8: Now lets enable CARP on the "Internal Network" i.e. LAN, select "Internal" > properties.







Step 9: Now once this is done we can "Tweak" the Load Factor for each "Array Member" according to our requirements.
Select Servers > Right click each "Array Member" > properties.
For this demo I will accept the default settings.





Step 10 : Click Apply in the above mentioned screen shot and it will prompt you to "Save & restart the services" > click ok.



We now have a Microsoft Internet Security and Acceleration Server (ISA Server) 2006 Enterprise Edition "Enterprise Array" configured for Cache Array Routing Protocol.

That's all !!!