Browser Is Slow to Respond When You Use an Automatic Configuration Script

When you add either one Internet Protocol (IP) address or a range of IP addresses that are listed in ISA Server, Proxy 2.0, Microsoft Threat Management Gateway Medium Business Edition, or Windows Essential Business Server 2008 to the default automatic configuration script that you want the browser clients to gain access to directly, you allow browsers to bypass the Web proxy server for that particular IP address range. In this scenario, the isInNet function is used.

The isInNet function queries a DNS server. When you either try to gain access to a DNS name or type the DNS name in the Address box in the browser, the browser queries either its locally configured DNS server or its locally configured WINS server to try to resolve the DNS name to an IP address. If the browser is successful, it tries to match the IP address that is returned by DNS or WINS with the IP addresses that are used in the automatic configuration script. If these addresses match, the browser gains access to that Web site directly. If these addresses do not match, the request is sent to the Web proxy server as an ordinary Web proxy request. However, if your organization does not allow browser client computers to directly resolve DNS names on the Internet, when the browser client that uses the IsInNet function initiates a local name resolution query, the query may be unsuccessful.

The length of delay that occurs when the name resolution query is unsuccessful depends on the name resolution mechanisms that your organization uses. When the name resolution query is unsuccessful, the browser skips the procedure in which the IP address that is retrieved by isInNet is matched. Instead, the browser sends an ordinary Web proxy request, which causes the Web pages to load but with a long delay.

The delay occurs only when the name resolution query is unsuccessful. If the clients are locally configured with a DNS server that can resolve all DNS names on the Internet, you do not experience a delay when the Web pages load.