How to enable the half-open TCP connections limit in Windows Vista with Service Pack 2 and in Windows Server 2008 with Service Pack 2

By default, the half-open TCP connections limit is disabled in Windows Server 2008 with Service Pack 2 (SP2) and in Windows Vista with Service Pack 2 (SP2). This article describes how to impose the half-open TCP connections limit in Windows Server 2008 with SP2 and in Windows Vista with SP2. The limit is ten connections.

Note In Windows Server 2008 and in Windows Vista with Service Pack 1 (SP1), the system allows for a maximum of ten half-open TCP connections at any time.

How to enable the half-open TCP connections limit

Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base: To enable the half-open TCP connections limit in Windows Server 2008 with SP2 or in Windows Vista with SP2, set the value of the EnableConnectionRateLimiting DWORD registry entry to 1 (0x00000001). To do this, follow these steps:

1. Click Start
   , type regedit in the Start Search box, and then click regedit.exe in the Programs list.
   If you are prompted for an administrator password or for confirmation, type your password, or click Continue.
2. Locate and then double-click the following registry key:
   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\EnableConnectionRateLimiting
3. In the Value data box, type 1, and then click OK.
4. Exit Registry Editor.
5. Restart the computer.