One of the main components of networking is the router. Without the “router”, the traffic would not be “routed” to its intended destination (duh!). That also means that the router is in a prime position to act as a gatekeeper to help protect the network. By defining and implementing Access Controls Lists (ACL’s), you can manage what IP addresses are allowed to communicate in or out of the network, and on what ports the communication is allowed. Using ACL’s, you can control or restrict traffic on the network, or you can create special ACL’s to use to log and troubleshoot traffic (for example checking traffic on a specific port to seek out infected devices on the network). TechRepublic has an informative article that will help you understand ACL’s- Cisco IOS Access Lists: 10 Things You Should Know. Another helpful resource is this 10-minute video demo on SearchNetworking.com by David Davis.