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After a proper SYN, SYN+ACK and ACK TCP-Handshake, the server immediately sends a FIN+ACK indicating a graceful connection closure. The client's HTTP requests results in RST packets from server. This happens once in a 100 concurrent calls. I have already investigated into SynAttackProtect parameter and Backlog Queue and these were related to connection resets, so unrelated to my problem. So in what cases will a Windows server suddenly issue a FIN, immediately after a successful TCP handshake?

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migrated from Jan 14 '13 at 18:37

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what exactly "immediately" stands for? – Jan Dvorak Jan 13 '13 at 14:04
@JanDvorak : After accepting the initial TCP Handshake with its SYN+ACK, the server sends a FIN+ACK packet to the client, thus gracefully closing the connection. The only HTTP request from the client was returned with an RST. – Narendran Thangarajan Jan 13 '13 at 16:02

Http.sys intermittently ends TCP/IP connections in Windows 7 or in Windows Server 2008 R2

Http.sys has been superseded since that hotfix was released. If you want a more current version:

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Thanks for the info. But in the above two cases you have mentioned, the connection is first closed by client. In my case, the server closes the connection with a FIN/ACK even before getting the first request from the client. – Narendran Thangarajan Jan 19 '13 at 4:02

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