Half-open limit fix (patch) for Windows



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 file tcpip.sys.

Microsoft first introduced this limit in Windows XP SP2 (Service Pack 2) and is present in all later versions of Windows. This was done to try to slow the spreading of viruses and malware from system to system and also to reduce the impact of infected systems participating in DoS (Denial of Service) attacks.

This limit 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.

Therefore, the speed of connection to other computers is actually limited.

P2P (peer-to-peer) programs (µTorrent, BitComet, eMule, P2P TV etc.) are generally the most affected programs. As they use up all 10 of the half-open connections, other Internet activity, especially the loading of web pages, can be extremely slow. The delay before the beginning of opening can make some tens seconds. This happens regardless of the speed of your Internet connection.

Half-open limit fix takes care of this problem by increasing the maximum limit of half-open connections. For the overwhelming majority of Internet users, changing the limit to 100 will be more than sufficient.