Microsoft has upgraded the Windows Vista tcpip.sys system file, which responsible for TCP/IP network connection protocol in Windows Vista, with several hotfixes and service pack. Originally both the 32-bit and 64-bit tcpip.sys is version 6.0.6000.16386 for Windows Vista RTM edition, and has since been updated to version 6.0.6000.20582, 6.0.6000.20583, 6.0.6000.20645 (by KB940646), 6.0.6001.16633, 6.0.6001.16659, 6.0.6001.17042 (v.658) and 6.0.6001.17052, with the later is what system with Windows Vista SP1 RC installed should have.

The update on tcpip.sys of Windows Vista also renders the patched version of tcpip.sys, which unlocks and removes the limit on simultaneous half-open incomplete (syn packets) connection attempts per second that can be made by system, to become unusable or causing system instability such as BSoD (Blue Screen of Death) or no Internet connection after patching. Attempt to patch newer version of tcpip.sys file does not work because once replaced, the patched tcpip.sys is rejected by Vista due to missing or corrupt digital signature.

Thus, a Chinese programmer named Eagle Twenty has developed a Windows Vista driver which loads independent of tcpip.sys. The driver, named CrackTcpip.sys, will installed as a CrackTcpip system service. When CrackTcpip.sys is ran, it will consistently monitor a memory address (offset 0x00059722 for Windows Vista SP1 RC v.668) which store number of the half-open TCP concurrent connection limit. The original value of the bit of 0A, which translate into 10. When CrackTcpip.sys service detects that the value for the TCP/IP simultaneous half-open connection limit is 0A, it will hack and change the value to FF, which is 255.

255 concurrent connections may looks small, but it’s actually already 25 times the original limit imposed by Microsoft. And the unlocked simultaneous TCP/IP sync packet limit probably enough to speed up performance of uploading and downloading, especially on peer to peer (p2) network such as BitTorrent (BT) and eDonkey2000 (ed2k). In some cases the patch will solve issues such as fail to load and open web page on web browser when using BT client to download in high speed with many torrents downloading, occupying and eating up all network resources, where users will have lots of log entries in Event Viewer that saying Event ID 4226 error.

CrackTcpip.sys Installation and Usage Guide

The package consists of 5 files:


Copy CrackTcpip.sys to \Windows\System32\Drivers\ folder.

To conduct a trial run of CrackTcpip.sys to test if the driver is compatible with your system, and does not cause any problem, error or BSoD, double click on TestInstall.reg to apply the registry value. Restart the computer, and then run TestRun.bat (or Run.bat) as administrator to start the service.

If there is any problem, reboot your computer to stop the CrackTcpip service. To uninstall, delete the CrackTcpip.sys from \Windows\System32\Drivers\ directory and run Uninstall.reg to remove the registry key.

To install CrackTcpip.sys, run Install.reg to autostart CrackTcpip service on every system startup. If you previously test run the CrackTcpip, there is no need to uninstall the test registry key first. The newer registry key will overwrite the old one. Again, run Run.bat (or TestRun.bat) to immediately activate the driver, or restart the computer. The service will start automatically on every boot up after adding keys in Install.reg.

To uninstall CrackTcpip after installing, run Uninstall.reg to remove the service registry key, restart PC, and then remove the CrackTcpip.sys file from \Windows\System32\Drivers\ folder.

Note that CrackTcpip.sys does not work in 64-bit Windows Vista (x64 edition), where Microsoft forces all drivers to be signed and certified by disable “bcdedit /set loadoptions DDISABLE_INTEGRITY_CHECKS” command which disables integrity check, failing all uncertified driver.

And, this version of CrackTcpipv668.sys is targeted to system with Windows Vista with Service Pack 1 RC, build 6.0.6001.17052 v.668, where the tcpip.sys should has the same 6.0.6001.17052 file version too. There is no guarantee that CrackTcpip.sys will work on any other versions of tcpip.sys.

Download (no longer required).

Update: Download for Windows Vista SP1 Refresh (v.744 or 6001.17128) and Refresh 2 (6001.18000 or RTM).

Use at your own risk, and in actual, less risk than previously patched tcpip.sys, as the external driver does not modify the code bits of tcpip.sys. Eagle Twenty, the developer of CrackTcpip.sys will develop a new version of CrackTcpip.sys if it no longer work (most likely) when final version of Vista SP1 is released in the next few weeks. Future release of CrackTcpip.sys, if the patch proves to be successful, will also be in the form of standalone executable, allowing user to install CrackTcpip in one click automatically.

Note: Since Windows Vista and Windows Server 2008 SP2, there is no more restriction (now unlimited) concurrent half open TCP/IP connection limit.