Web Sites May Not Be Loaded If Viewed from Behind ISA Server (322597)


The information in this article applies to:

  • Microsoft Internet Security and Acceleration Server 2000
  • Microsoft Internet Security and Acceleration Server 2000 SP1
This article was previously published under Q322597

SYMPTOMS

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.

CAUSE

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.

STATUS

This behavior is by design.

MORE INFORMATION

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:

http://www.w3.org

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Modification Type:MajorLast Reviewed:7/24/2002
Keywords:kbenv kbprb KB322597
©2002 Microsoft Corporation. All rights reserved.