Half-Open Limit Fix is an application used for managing TCP connections. It was initially released on May 25, 2012. The program is used to bypass the TCP stack connection limit implemented by Microsoft in its Windows tcpip.sys file. Microsoft first introduced the TCP connection limit in Windows XP SP2. Its primary purpose is to stop the spread of malware and viruses from one system to another by setting a maximum of 10 concurrent half-open outbound connections. After the 10 limit, other connection attempts will be placed in queue. This limit could affect the Internet connection speed. Since some programs tend to consume all of the 10 half-open connections, other activities that require an Internet connection can become affected.
The program works by increasing the upper limit value of the half-open outbound TCP (Transmission Control Protocol) connection attempts. Instead of the maximum 10 given by Microsoft, this application allows the limit to be changed to any value. The program’s interface is clear-cut. It’s a single dialog box with three buttons (i.e. Refresh, Add to tcpip.sys and Restore Original File). After choosing the new limit, users only have to click on the “Add to tcpip.sys” button and restart the computer to apply the changes made. Aside from changing the limit, the application also has the ability to create a backup copy of the original tcpip.sys file. This backup copy allows the original file to be restored at any time using the Restore Original File button.