This paper presents the review of the network monitoring technologies that now are widely used. The main attention is given to MRTG, NETMON and NFC&NDA systems. The paper describes their advantages, configuring parameters and a necessary programming base. The experience of using these systems for monitoring the NSCnet network is discussed. A special attention is given to the issues of measurement and analysis of the traffic that concerns certain groups of users and control points of the network. Also, this paper describes how the monitoring, the data collecting and the traffic analyzing systems are used in the SB RAS (Siberian Branch, the Russian Academy of Sciences) Internet.