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How do I remove XP SP2's limitation on outgoing TCP connection attempts?



Microsoft has introduced a new security feature with the release of Windows XP SP2 that limits the number of possible TCP connection attempts per second to 10 (was unlimited before). This feature can possibly affect programs that make heavy use of TCP/IP connections, e.g. Paessler's Webserver Stress Tool and PRTG Network Monitor.

How do I patch my system to remove the limitation?

connections error general limit networking prtg tcp webserver-stress-tool windows windows-xp

Created on Feb 9, 2010 2:56:32 PM by  Daniel Zobel [Product Manager]

Last change on Feb 23, 2010 5:30:06 PM by  Daniel Zobel [Product Manager]

1 Reply

Accepted Answer



The Problem

With 10 new connections per second you can still create 600 connections per minute, but this is still not enough for a load testing tool like Webserver Stress Tool, or when monitoring large networks with PRTG Network Monitor.

If you experience event ID 4226 in your event log or receive the message "TCP/IP has reached the security limit imposed on the number of concurrent TCP connect attempts" while running Webserver Stress Tool you must make changes to your Windows installation!

Unfortunately there exists no REG-key which could easily be set. The only way to get rid of this limitation is to apply a patch to the TCP/IP Windows library. The file TCPIP.SYS in the directory C:\WINDOWS\SYSTEM32\DRIVERS and C:\WINDOWS\SERVICEPACKFILES\I386 has to be changed (system dependend eventually in C:\WINDOWS\SYSTEM32\DLLCACHE, too).

The Solution

To change or remove the limit, you can use the following program: Event ID 4226 Patcher v2.x - A patching program for removing or changing the limit imposed on connection attempts in SP2. The patcher has the ability to restore tcpip.sys back to the original... Still, you might want to back up tcpip.sys, use it at your own risk.

The URL of the download page is: http://www.lvllord.de/?lang=en&url=downloads

(The author of this patch can be reached at www.lvllord.de).

This program increases the value from 10 half-open connections to 50 and the CRC is been corrected. The value can be changed during runtime and with the parameter /L.


Just download the patcher and execute it. It will automatically find the windows directory and ask you if it should increase/decrease the value. For higher values than 50, please check the help with parameter /?. After a successful patch, the new TCPIP.SYS will be automatically installed. After that, the computer should be restarted.


The operating systems Windows XP and Windows Server 2003 are not officially supported anymore. If you run PRTG on one of these operating systems, you have to accept limited monitoring functionality. We do not provide support for any issues that might be caused (directly or indirectly) by using these Windows versions.

Created on Feb 9, 2010 2:58:02 PM by  Daniel Zobel [Product Manager]

Last change on Aug 25, 2014 4:51:48 PM by  Gerald Schoch [Paessler Support]

Disclaimer: The information in the Paessler Knowledge Base comes without warranty of any kind. Use at your own risk. Before applying any instructions please exercise proper system administrator housekeeping. You must make sure that a proper backup of all your data is available.