A virtual laboratory is a virtual space where students are able to carry out practical activities. This paper presents an integrated structure for a virtual laboratory consisting on nine resources divided into pedagogical, human, and technological factors. Such a structure is based on the experience gained in design and development of virtual laboratories during the past 11 years in a virtual university. The proposed structure has been applied to different virtual laboratories, and this paper presents the special case of a virtual networking laboratory (VNLab) where students can access real networking devices. The VNLab structure described in this paper has been used at the Open University of Catalonia for the Cisco Networking Academic since 2001. Its suitability has been evaluated by the students using a Web questionnaire, and its correctness for the industrial electronics field has been analyzed.