Access control List (ACL)

Access control lists (ACLs) are one of the fundamental building blocks of a network configuration. If you fully understand how Access lists are constructed and used, you're well on your way to providing adequate security to your network. However, if you fail to grasp how wildcard masks are used or how the order of operation affects Network Address Translation (NAT), then you could very well make your network the next successful target of a hacker. Understanding this topic is important, both for the test and for your career.

Access control lists (ACLs) are used throughout many IT security policies, procedures, and technologies. An access control list is a list of objects; each entry describes the subjects that may access that object. Any access attempt by a subject to an object that does not have a matching entry on the ACL will be denied. Technologies like firewalls, routers, and any border technical access device are dependent upon access control lists in order to properly function. One thing to consider when implementing an access control list is to plan for and implement a routine update procedure for those access control lists.