Skip to main content

Overcoming TCP/IP Connection Limits

If you are using a high number of TCP connections, particularly with a high connect/disconnect rate, you may exhaust the number of available ports as they may all be in the TIME_WAIT state.

There are two actions that can prevent this:

  • Increasing the number of available (ephemeral) ports.
  • Reducing the TIME_WAIT timeout period.

Increasing the Number of Available (Ephemeral) Ports​

By default Windows only allocates ephemeral ports in the range 1024 through 4999.

To increase the upper range of ephemeral ports that are dynamically allocated to client TCP/IP socket connections perform the following. You should first save a backup of the registry.

  1. Start the Registry Editor.

  2. Browse to, and then select the following key in the registry:

    HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters

  3. Create a new DWORD value, or modify the existing value of MaxUserPort to increase the number of ephemeral ports that can by dynamically allocated to clients:

    • Value name: MaxUserPort
    • Value data: <Enter a decimal value between 5000 and 65534>

  4. Save the changes and close the Registry Editor.

warning

You must restart your computer for this change to take effect.

Reducing the TIME_WAIT Timeout Period​

This setting determines the length of time that a connection will stay in the TIME_WAIT state before being closed. The default is 240 seconds which on a busy server will limit the maximum connections to around 200/sec. Reducing this setting will increase the maximum connection limit.

  1. Start the Registry Editor.

  2. Browse to, and then select the following key in the registry:

    HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters

  3. Create a new DWORD value, or modify the existing value of TcpTimedWaitDelay to alter the TIME_WAIT duration:

    • Value name: TcpTimedWaitDelay
    • Value data: <Enter a decimal value between 30 and 300 seconds>

  4. Save the changes and close the Registry Editor.

warning

You must restart your computer for this change to take effect.

Last updated on