In this chapter, we went through the basics of blocking, including terminology, devices, and device and system requirements. Then, we went through guidelines that you should follow when implementing a blocking solution. We looked at how pre-block, post-block, and blocking ACLs work together to form the non-blocking and blocking ACLs and what to consider when deciding to which interface and direction you should apply the ACLs. We then went through blocking configuration steps for IOS Routers, PIX Firewalls, and Catalyst OS switches as managed devices. Finally, you learned how you can implement and configure master blocking to provide a better intrusion-detection implementation for many network environments.