Prior to SP2, if a requested destination name was in the list, it was accessed directly. With SP2 - a requested name in the list is accessed directly, unless IP addresses are included in the list. In that case, an attempt is made to resolve the site name to an IP address. Access is direct only if the resolved IP address is found in the list.
There have been lots of questions from customers on how to make ITunes work after applying ISA Server Service Pack 2.
First of all, some background on what’s happening. A server might return a compressed response (with an "Content-Encoding: gzip "HTTP header) even though ISA Server did not specifically request compressed data. For security reasons, if the ISA Server compression settings are not enabled to Request compressed HTTP content from servers, then ISA Server will deny the response.
This is what’s happening with ITunes.
The good news: the music can go on…You can configure ISA Server so that ITunes will work. Here’s how:
On the General node, click Define HTTP Compression Preferences.
On the Settings tab, add a computer set that includes the IP address of the site to the list.
Select the site and click Set Compression.
Enable Request compressed HTTP content from servers.
Let the music play!
ISA Server Product Team