Network Monitoring tool monitors the system and sends a report to the administrator if an error or fault occurs. It is a part of network management system and collects data from all possible network elements.The various network monitoring fields are Packet analyzer, application and service monitor, intrusion detection etc. These are performed with the help of network monitoring tool. Ping is the basic network monitoring tool. The best network monitoring tools are Nagios, Icinga, Anturis, PRTG, Monitis etc. The command line tools include top, nmap, netstat, atop, mytop etc.