another1 great tool is Half-open limit fix (patch) for Windows
http://half-open.com/home_en.htm
Half-open limit fix is a program designed to change the maximum number of concurrent half-open outbound TCP connections (connection attempts) in the Windows system tcpip.sys file.
Microsoft first introduced this limit in Windows XP SP2 and it is present in later versions, which purpose is to try to slow the spread of virus and malware from system to system, and also to reduce the impact of infected systems participating in DoS (Denial of Service) attacks.
Microsoft's limiter makes it impossible for Windows systems to have more than 10 concurrent half-open outbound connections; after 10, new connection attempts are put in a queue and forced to wait. Thus, the speed of connection to other PCs is limited.Therefore, the speed of connection to other computers is actually limited.
P2P (peer-to-peer) programs like µTorrent, BitComet, eMule, P2P TV, etc.,are generally the programs mostly affected. Since bittorrent apps tend to use up all 10 of the half-open connections, other Internet activity—especiallythe loading of web pages—can become extremely slow. The delay before opening a new page can take over ten seconds: this delay occurs regardless of your Internet connection speed.
Half-open limit fix remedies this problem by increasing the maximum limit of half-open connections. For most Internet users, changing the limit to 100 will be more than sufficient.
Is the program safe?
Half-open limit fix creates a backup copy of the edited tcpip.sys file, so you can at any moment restore the original file at the press of a button. I have tried to make the program as safe as possible but cannot offer any guarantee. Use program at your own risk.
What is the optimal value of concurrent half-open outbound connections limit?
I consider the optimal value to be an equal 100. Increasing the limit will have effect only if you run several P2P programs simultaneously (e.g., µTorrent, BitComet, eMule, P2P TV, etc.), or your PC works as a server.
Does the limit cut down my Internet speed?
To check whether this limit cut down your Internet speed, look in Windows Event Viewer (Start -> Control Panel -> Administrative Tools; or Start -> Run -> EventVwr.msc). Each message {EventID 4226: TCP/IP has reached the security limit imposed on the number of concurrent TCP connect attempts} reports if the limit has worked. Usually it means that the network worm (virus) or any P2P program works on your PC. If such messages in Event Viewer appear, most likely you garnered a problem and will have difficulties opening web pages in a browser.
The program started for the first time, but it shows 50/1000/16777214 half-open connections, instead of 10 by default. What does it mean?
Most likely you are using an unofficial Windows build in which the maximum quantity of half-open connections is already increased in the tcpip.sys driver. Also, maybe you used a foreign patch, which has changed this value. If you don't have new events 4226, you may decrease this limit or not change it.
Why in Windows 7 and Vista the limit can be from 1 to 255 and infinity?
Because in these operating systems, limit is stored in 1 byte in the tcpip.sys file. That is, it can accept values from 0 to 255. Even if at value 255 new events 4226 continue to appear, you can set the value to infinity (∞). That means switching-off the limit of simultaneously half-open connections.
Does the limit of concurrent half-open connections present in Windows Server 2003/2008, Vista SP2 and Windows 7 beta start from build 7100?
No. It is physically present in the tcpip.sys file but has no effect; thereby, there is no Event ID 4226 or Internet deceleration when a P2P program runs in this versions of Windows.
Download: http://half-open.com/download_en.htm
direct: http://half-open.com/Half-open_limit_fix_4.1.exe
