Top Linux commands to monitor NETWORK

Monitoring the system & its resources is one of the most important tasks for a system admin & we should be aware of it. There are plenty of 3rd party tools like Nagios, Zabbix etc that we can use for complete system monitoring & are extremely useful when dealing with a number of systems. But if you have a single or less number of systems, then the best approach would be to use the Linux in-built monitoring commands.