Creating access lists is really a lot like programming a series of if-then statements—if a given
condition is met, then a given action is taken. If the specific condition isn’t met, nothing happens
and the next statement is evaluated. Access-list statements are basically packet filters that
packets are compared against, categorized by, and acted upon accordingly. Once the lists are
built, they can be applied to either inbound or outbound traffic on any interface. Applying an
access list causes the router to analyze every packet crossing that interface in the specified
direction and take the appropriate action.