Data type


Default value


0–255 ( retransmission attempts )



Determines how many times TCP retransmits an unanswered SYN-ACK (connection request acknowledgment). TCP retransmits acknowledgments until they are answered or until this value expires. This entry is designed to minimize the effect of denial-of-service attacks (also known as SYN flooding ) on the server.

This entry also determines, in part, whether the SYN attack protection feature of TCP is enabled. This feature detects symptoms of SYN flooding and responds by reducing the time the server spends on connection requests that it cannot acknowledge. SYN attack protection is enabled when the value of the SynAttackProtect entry is 1 and the value of this entry is at least 2.

TCP/IP adjusts the frequency of retransmissions over time. The delay between the first and second retransmission is three seconds. This delay doubles after each attempt. After the final attempt, TCP/IP waits for an interval equal to double the last delay, and then it closes the connection request.

Note Image Note

Windows 2000 does not add this entry to the registry. You can add it by editing the registry or by using a program that edits the registry.

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