Cisco® Secure Internet Security Solutions

Access Lists

Access lists are created to deny certain packets the ability to traverse a router interface. By default, a router will allow all packets to travel through an interface. The router may not know where to forward a particular packet but will still allow that packet to cross the interface. An access list is a list of packets that is consulted before allowing or disallowing a packet to travel forward toward its ultimate destination.

Although this text assumes that you have at least an understanding of access lists, this section contains a brief review of the basic forms of IP access lists before moving onto the more complex reflexive and context-based access lists. The examples within this chapter will focus on IP access lists. A wide ...