Web Sites May Not Be Loaded If Viewed from Behind ISA Server

Some Web sites may be only partially loaded, or may generate script errors, when you view them from behind an Internet Security and Acceleration (ISA) Server 2000-based server. If you bypass the ISA Server-based server, the site is loaded correctly. This behavior is more likely to occur if you are using Microsoft Internet Explorer.

Web sites that generate dynamic content by using HTTP 1.1 encoding frequently compute an inaccurate content length. The content length must match the size of the HTTP data that is returned in response to a client request. ISA Server closes an HTTP session after it receives the data size that is specified in the Content-Length field of the HTTP response packet. If the computed content length is smaller than the actual data set that is returned, ISA Server drops the remaining data. This data may be an image or another component of the page. At other times, it may not be obvious that a partial page has been returned to the client. You can use a network trace from a tool such as Network Monitor to confirm this condition.

This behavior is by design.

This behavior prevents a buffer overrun on the client. You can turn off the HTTP Application Filter to permit a site to be viewed from behind ISA Server, but note that doing so compromises security and prevents HTTP caching.

Based on RFC 2616, the content length must be computed correctly for a data set. Use "chunked" encoding if the message length cannot be determined in advance. This must be performed on the Web site that hosts the content. For additional information about RFC 2616, visit the following World Wide Web Consortium Web site: Microsoft provides third-party contact information to help you find technical support. This contact information may change without notice. Microsoft does not guarantee the accuracy of this third-party contact information.