Enabling the Cache Array Routing Protocol on the Array

  • Article

The Cache Array Routing Protocol (CARP) significantly enhances the basic Web caching capabilities found in ISA Server 2004 Standard Edition. 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 amount of disk space you need to dedicate to the Web cache and significantly increases the amount of content you can cache per unit disk space configured for the array.

ISA Server 2004 Enterprise Edition Web caching arrays also provide for load balancing and fault tolerance. When the Web Proxy clients are configured with the autoconfiguration script (which can be done so that the ISA Server firewall administrator never needs to interact with client computers), they are able to correctly identify which ISA Server firewall array member is responsible for Web content that they want to retrieve. The Web Proxy client sends a request to the array member responsible for the content. This client-side routing feature enhances the array’s load balancing capabilities because it ensures that no array member is ever overburdened with a disproportionate number of Web requests.

In this section, you will enable CARP to create an ISA Server 2004 Enterprise Edition Web caching array. You will complete the following procedures:

  • Create cache drives on the array. The array Web cache is stored on a disk file located on the hard disk of each member of the ISA Server 2004 Enterprise Edition Web caching array. You will use the ISA Server 2004 Enterprise Edition console on the management station to create the Web cache disk files on each array member.
  • 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. You will enable the Web Proxy listener using ISA Server Management.
  • 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 internal network interfaces of the array.
  • Enable automatic discovery on the Internal network Web listener. 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 autoconfiguration information.
  • Configure Web browsers to use the autoconfiguration script through automatic discovery. The autoconfiguration script enables Web Proxy clients to determine which member of the Web caching array is responsible for the requested Web content. This enables the Web Proxy clients configured with the autoconfiguration script to determine in advance the correct array member to send the Web request to. This is client-side Web routing, and it can significantly improve overall Web performance.

Create Cache Drives on the Array

Web caching is disabled by default on ISA Server 2004 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:

  1. At the enterprise management station on the Internal network, open the ISA Server 2004 Enterprise Edition console, expand the array name, and then expand the Configuration node in the left pane of the console. Click the Cache node.
  2. Right-click the array-1 entry in the details pane and click Properties.
    Cc302524.c16fe70b-6af9-4425-a16f-3eed08574a54(en-us,TechNet.10).gif
  3. In the array-1 Properties dialog box, enter a value for the size of the cache file on the array-1 computer. In this example, you create a 100 megabyte (MB) cache file. Enter 100 in the Maximum cache size (MB) text box and click Set. Click Apply, and then click OK.
    Cc302524.4b500bdd-e336-441b-bbe6-8f061729ac02(en-us,TechNet.10).gif
  4. In the details pane, right-click array-2 and click Properties.
  5. In the array-2 Properties dialog box, enter the value for the size of the cache file on the array-2 computer. In this example, you create a 100 MB cache file. Enter 100 in the Maximum cache size (MB) text box and click Set. Click Apply, and then click OK.
    Cc302524.3a73a78f-d6b4-4916-8f74-1f03f8e2056b(en-us,TechNet.10).gif
  6. The size of the cache files appears in the Cache Size on NTFS Drives (MB) column in the details pane.
    Cc302524.b45e603b-6a42-4deb-b977-0ea4aa4c6e3b(en-us,TechNet.10).gif

Enable the Web Proxy Listener on the Intra-Array Network Interfaces

The Web Proxy listener must be enabled on the interface used for intra-array communications. Perform the following steps to enable the Web Proxy listener on the intra-array communication network interface:

  1. In the ISA Server 2004 Enterprise Edition console, click the Networks node located under the Configuration node.
  2. In the details pane, right-click the Intra-array Network entry and click Properties.
  3. Click the Web Proxy tab. On the Web Proxy tab, select the Enable Web Proxy clients check box.
    Cc302524.9f25f8e5-4e5f-4ca4-aabf-0ad9da0a23e9(en-us,TechNet.10).gif
  4. Click Apply. Do not close the Intra-array Network Properties dialog box.

Enable CARP on the Array

The next step is to enable CARP on the ISA Server 2004 Enterprise Edition Web caching array. Perform the following steps to enable CARP on the array:

  1. In the Intra-array Network Properties dialog box, click the CARP tab.
  2. On the CARP tab, select the Enable CARP on this network check box.
    Cc302524.3db08b71-6ee2-46b4-a852-434d5b4af3ea(en-us,TechNet.10).gif
  3. Click Apply, and then click OK.
  4. Click Apply to save the changes and update the firewall policy.
  5. In the ISA Server Warning dialog box, select the Save the changes and restart the services option and click OK.
  6. Click OK in the Apply New Configuration dialog box.

Enable Automatic Discovery on the Internal Network Web Listener

For the Web Proxy clients to fully take advantage of CARP, you should enable the Web Proxy clients to perform client-side Web routing. Client-side Web routing enables the Web Proxy clients to know which ISA Server 2004 Enterprise Edition array member is responsible for the Web object requested. The Web Proxy clients must be configured to obtain Web routing information from the array to perform client-side routing.

There are two methods you can use to configure the Web Proxy clients to perform client-side routing: Configure a Web Proxy Automatic Discovery (WPAD) entry in DNS or Dynamic Host Configuration Protocol (DHCP), or configure the browsers to use the autoconfiguration script. To take advantage of automatic discovery, the array must be able to publish automatic discovery information to WPAD clients.

Perform the following steps to enable the array to publish automatic discovery information:

  1. In the ISA Server 2004 Enterprise Edition console, click the Networks node in the left pane of the console. Click the Networks tab in the details pane and right-click the Internal network. Click Properties.
  2. In the Internal Properties dialog box, click the Auto Discovery tab.
  3. On the Auto Discovery tab, select the Publish automatic discovery information check box. Leave the default Use this port for automatic discovery requests port at 80.
    Cc302524.2cb48bbf-3c1c-4884-b178-2a0027be2d49(en-us,TechNet.10).gif
  4. Click Apply, and then click OK.
  5. Click Apply to save the changes and update the firewall policy.
  6. Click OK in the Apply New Configuration dialog box.

Configure Web Browsers to Use the Autoconfiguration Script Through Automatic Discovery

The default setting for Internet Explorer is to use automatic discovery to obtain information from the Web caching array. However, for the Web browser to automatically obtain this information, a WPAD entry must be configured in DNS or DHCP. For more information about configuring WPAD entries, see the instructions in Automatic Discovery for Firewall and Web Proxy Clients at https://www.microsoft.com/technet/prodtechnol/isa/2004/plan/automaticdiscovery.mspx.

In this ISA Server 2004 Enterprise Edition Quick Start Guide, you will manually configure the browser to obtain the autoconfiguration script. If the Web Proxy client computers are part of an Active Directory domain, you can configure Group Policy to automatically configure the Web browsers to use the autoconfiguration script without requiring WPAD entries.

Perform the following steps to configure the browser on the dc.msfirewall.org computer:

  1. Open Internet Explorer, click the Tools menu and then click Internet Options.
  2. In the Internet Properties dialog box, click the Connections tab.
  3. On the Connections tab, click the LAN Settings button.
  4. In the Local Area Network (LAN) Settings dialog box, clear the Automatically detect settings check box and select the Use automatic configuration script check box. In the Address text box, enter https://10.0.0.1:8080/array.dll?Get.Routing.Script. Click OK.
  5. Click OK in the Internet Properties dialog box.

[Topic Last Modified: 02/26/2008]