17

Jun

2009

WinXP SP2/VISTA limits max. number of TCP connections/second

Windows XP Service Pack 2 will limit the maximum number of TCP connections your computer can have at one time. I can see what they are thinking, but I wont mind unless some of my applications (like my multi-threaded port scanner) wont work correctly with this new setting.

Here is a registry edit you can do to increase the max:

TcpNumConnections

Key: Tcpip\Parameters
Value Type: REG_DWORD – Number
Valid Range: 0 – 0xfffffe
Default: 0xfffffe
Description: This parameter limits the maximum number of connections that TCP can have open at the same time.

TcpWindowSize

Key: Tcpip\Parameters
Value Type: REG_DWORD – Number of bytes
Valid Range: 0 – 0xFFFF
Default: The smaller of 0xFFFF
OR
(The larger of four times the maximum TCP data size on the network
OR
8192 rounded up to an even multiple of the network TCP data size.)
The default is 8760 for Ethernet.
Description: This parameter determines the maximum TCP receive window size of the computer. The receive window specifies the number of bytes a sender can transmit without receiving an acknowledgment. Generally, larger receive windows improve performance over high (delay * bandwidth) networks. For highest efficiency, the receive window must be an even multiple of the TCP Maximum Segment Size (MSS).

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