Lessons learned from complex hands-on defence exercises in a cyber range

We need more skilled cybersecurity professionals because the number of cyber threats and ingenuity of attackers is ever growing. Knowledge and skills required for cyber defence can be developed and exercised by lectures and lab sessions, or by active learning, which is seen as a promising and attractive alternative. In this paper, we present experience gained from the preparation and execution of cyber defence exercises involving various participants in a cyber range. The exercises follow a Red vs. Blue team format, in which the Red team conducts malicious activities against emulated networks and systems that have to be defended by Blue teams of learners. Although this exercise format is popular and used worldwide by numerous organizers in practice, it has been sparsely researched. We contribute to the topic by describing the general exercise life cycle, covering the exercise's development, dry run, execution, evaluation, and repetition. Each phase brings several challenges that exercise organizers have to deal with. We present lessons learned that can help organizers to prepare, run and repeat successful events systematically, with lower effort and costs, and avoid a trial-and-error approach that is often used.