There could be many reasons, but the most common are:
- The port is not open on the destination machine.
- The port is open on the destination machine, but its backlog of pending connections is full.
- A firewall between the client and server is blocking access (also check local firewalls).
- IP address conflict
After checking for firewalls and that the port is open, use telnet to connect to the ip/port to test connectivity.
For Example
Test Connectivity
telnet 10.1.131.19 4447
Check the port status of remote system
netstat -npl | grep 4447
Check firewall
tcpdump -n icmp
Check IP
arping 10.1.131.19
Check the number of active connections
netstat -np | grep -w 4447 | grep ESTABLISHED | wc -l
Increasing the maximum number of tcp/ip connections in linux