Abstract: Traditional network experiment of colleges and universities cannot be carried out due to restrictions of place, equipment costs and class hour. It seriously affects understanding of the basic principles for the network and practical ability to exercise for students. A detailed description of the network experiment in virtual environment is given by configuration example on network load balancing using GNS3 in order to solve the traditional problems of network experiment.

Key words: network experiment, GNS3, virtualization, IGRP, load balancing