Microsoft KB Archive/287705

= Internet Explorer Connection Does Not Succeed with Content-Length Checking Through Proxy Server =

Article ID: 287705

Article Last Modified on 1/31/2007

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APPLIES TO


 * Microsoft Internet Explorer 5.5 Service Pack 1
 * Microsoft Internet Explorer 5.01
 * Microsoft Internet Explorer 5.5 Service Pack 1
 * Microsoft Internet Explorer 5.01
 * Microsoft Internet Explorer 5.5 Service Pack 1
 * Microsoft Internet Explorer 5.01
 * Microsoft Internet Explorer 5.5 Service Pack 1
 * Microsoft Internet Explorer 5.01

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This article was previously published under Q287705



SYMPTOMS
Internet Explorer may not attempt to retry an unsuccessful connection through a Proxy server when using Proxy Keep-Alives.



CAUSE
If a Web server sends more data than is indicated in the Content-Length header, the Proxy server may determine that this is a violation of the use of the Content-Length header, according to RFC 2068 Section 14.14, and 4.4. Therefore, it will close the port that is being used to download the data. If the port was opened by Internet Explorer using the Proxy-Connection:Keep-Alive header, the Proxy server will indicate that the port is being closed by setting the TCP FIN Flag in the final response frame on the given port.

Internet Explorer will use the Content-Length header to determine the amount of data to receive from the TCP socket. After this happens, there is extra data left in the socket that would normally be discarded. However, because the Keep-Alive session is in progress, this TCP socket will be re-used. When attempting to re-use the TCP socket for subsequent HTTP requests, the Proxy server will issue a TCP Reset on the port because it closed the port previously, due to the Content-Length mismatch.



RESOLUTION
To resolve the issue, use Network Monitor to verify that the Content-Length issued by the Web server is smaller than the physical bytes of data of being sent. If this condition exists, please contact the owner of the Web server, and indicate that the Web server is sending more data than is indicated in the Content-Length header, and request that they resolve the issue at the Web server.



MORE INFORMATION
For additional information about the use of Network Monitor, click the article number below to view the article in the Microsoft Knowledge Base:

148942 How to Capture Network Traffic with Network Monitor

