Monitoring of Network

You can use snmpd and cacti

Check out this guide

There are a lot of monitoring solutions out there.

Munin might be an option for your needs, take a look at sysstat and use kSar to visualize the results.

Your choice depends on the needs you have.

karthick87 has the answer, but just to amplify it your monitoring has to be distributed amongst the 300 end-stations and cannot be simply centralized to one point.

The biggest reason this is necessary is that you are probably using a switched (not shared) network hub so no single point is capable of seeing all the traffic on the net. SNMP is certainly old-school, partly because it works.