I have a custom server in C# being run on Ubuntu 9 under mono. I can make up to 15 silverlight clients connect to the server. When I make the 16th, it just waits. And if I close one of the established connections, the 16th client is able to connect. I am making the connections from one machine. I am also not exceeding any file handle limit. The limit is 1024 and I am having around 300. Any ideas how to make more connections? Also why the number 15? Is it something linux-specific? EDIT: I have run the same server on an Ubuntu 11.10 virtual machine and was able to make more than 15 connections. I presume it's a configuration problem on the Ubuntu 9 machine then. Any help on that?