There is a limit on the number of concurrent socket connections that an application can accept in BSD, Windows, and other operating systems. This is set at compile time, but it can be overridden. Here is a discussion of this limitation by Microsoft, and here is further discussion. One application that is sticking this on its ear is Nginx.
Paul is an Avid Tech Geek who Loves writing, Cycling and All Things Linux! He comes from a Background of Windows Administration along with Ubuntu/Centos Server administration.