I write a multiple threads client program to send information  to 4 server, when i test point to point , that 's ok. But when i test the 1 to 4, problem display : socket No route to host. Then through some research the socket principle, I found that the c/s ,both should be shut off the firewall. My platform is Fedora and CentOS , U just net to type 'setup' in terminal, choose the 'Firewall configuration' and disable it.