Officially, the incomplete half-open outbound TCP connection attempts allowed at any one time is now unlimited by default in Windows Server 2008 and Vista SP2 (Service Pack 2), and Windows 7. Actually, the ability to limit or restrict number of half-open outgoing TCP connections system can create or establish is built into Windows Vista SP2 and Windows 7, however it’s disabled by default.

Thus, in most circumstance, no more Event ID 4226 in Windows Vista SP2 or Windows 7 (note: Windows Server always doesn’t have half-open TCP connections limit). No patch of any kind is required, for kernel memory or tcpip.sys file. In the event that you want to doubly confirm that the half-open TCP connections limit is indeed been removed, or system administrator has placed a limit restriction on half-open incomplete TCP connections, it’s possible to configure or use EnableConnectionRateLimiting registry key to disable and remove the half-open TCP connections limit.

How to Disable Half-Open TCP Connections Limit in Windows Vista with SP2 or Windows 7

  1. Click Start button.
  2. Type regedit in the Start Search box, and then click regedit.exe in the Programs list.
  3. If you are prompted for an administrator password or for confirmation, type your password, or click Continue.
  4. Navigate to the following registry key:

    HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
    Services\Tcpip\Parameters\

  5. In the right pane, locate EnableConnectionRateLimiting registry value data entry.
  6. If “EnableConnectionRateLimiting” is not found, the half-open TCP connections limit is already removed/disabled, allowing unlimited half-open incomplete outbound connections.

    If “EnableConnectionRateLimiting” is found, delete the registry entry away, or double click on EnableConnectionRateLimiting, and in the Value data box, type 0, and then click OK.

    Note: If you want to have the registry key to exist, create a new DWORD (32-bit) Value named as EnableConnectionRateLimiting, and set it to 0 to continue disable and bypass the limit check.

  7. Exit Registry Editor.
  8. Restart the computer (in fact, the change takes effect immediately without the need to reboot).

The registry key hack to disable half-open TCP connections limit works on all 32-bit (x86) and 64-bit (x64) edition of Windows Vista with SP2 and Windows Server 2008 with SP2, and unofficially, Windows 7.

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