In the teaching of computer networks the main problem that arises is the high price and limited number of network devices the students can work with in the laboratories. Nowadays, with virtualization we can overcome this limitation. In this paper, we present a methodology that allows students to learn advanced computer network concepts through hands-on experience with the VNUML-UM virtualization tool, which is offered freely as a resource for the practical teaching of mobility, load balancing, and high availability. To verify the utility of using the VNUML-UM virtualization tool in the teaching of advanced computer network concepts, we have performed some opinion polls to the students during the last three academic years. The obtained results confirm that our students agree that the VNUML-UM enables an enhanced learning process of the different concepts and their practical skills. This perception is also confirmed by the final marks obtained by the students, which have considerably improved along the years. To the best of our knowledge, this paper presents the first experience that provides results on the use of virtualization to teach advanced concepts in the field of computer networks.