Modified Features

Several ISA Server 2004 features have been modified in this service pack. The changes to these features are described in this topic.

Cache Array Routing Protocol

In ISA Server 2004 Enterprise Edition, the Cache Array Routing Protocol (CARP) mechanism used hash-based routing that depended on the URL to determine which array member would handle the request. CARP exceptions were the sites that you wanted to be handled by a single array member. The array member that was assigned to handle the request was selected based on the host name as it appeared in the host header. This has changed in Service Pack 2, to better complement Internet Explorer functionality and provide better control over the distribution of requests that produce heavy Web traffic.

In Service Pack 2, the CARP hash-based routing uses the host name to determine which array member handles the request. CARP therefore assigns all of the requests for a particular host, such as www.fabrikam.com, to a specific array member. This also maintains the context of the session, as the requests and responses are handled by a single array member. CARP exceptions are the sites that you want to be distributed to all array members, because they generate too much traffic to be handled by a single array member. For example, you may want all Microsoft update requests to be distributed, and not assigned to a single array member. You would therefore add the Microsoft Update site to the list of CARP exceptions.

Auto Detection

The behavior of client auto detection as configured on ISA Server has been modified in this service pack. With Service Pack 2, a request has to match both the IP address range and the server name or domain name provided on the Web browser tab to bypass the proxy.

Tracing

Service Pack 2 includes an error-level tracing mechanism that operates continually in the background. If necessary, the tracing information is available for Microsoft Product Support Services. The tracing mechanism does not collect personally identifiable information.

Tracing takes place in the background, and has a negligible affect on ISA Server performance. A 400 megabyte (MB) file (%windir%\debug\isalog.bin) is created by Service Pack 2 on each computer running ISA Server services, to contain the tracing information.

We recommend that you use the default settings for this feature. However, if you want to modify the tracing mechanism, you can do so through the registry key HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\ISATrace. To change the size of the file used by tracing, change the value of CircularlLogSizeMB. To disable tracing, change the BootTracing value to 0. This does not delete the file, which has to be deleted manually. After registry changes, restart the computer so that the changes take effect. If you create the registry key before installing Service Pack 2, and set the BootTracing value to 0, the tracing file will not be added during the installation, and tracing will not be enabled.

Authentication Security

When you use HTTP-to-HTTP bridging, ISA Server will not allow traffic on the external HTTP port when the Web listener is configured to request Basic, forms-based, or Remote Authentication Dial-In User Service (RADIUS) authentication. This is a security-related change. These credentials should be encrypted, and not sent in clear text over HTTP.

[Topic Last Modified: 12/16/2008]