The last few chapters introduced you to routing protocols and their basic configuration.
By default, once you set up routing, your router will allow any packet to flow from
one interface to another. You may want to implement policies to restrict the flow of
traffic, for either security or traffic policy reasons. Cisco allows you affect the flow of traffic from
one interface to another by using access control lists (ACLs). ACLs, pronounced ackles, are a
very powerful feature of the IOS. Cisco actually supports ACLs for other protocols besides IP,
including IPX, XNS, DECnet, AppleTalk, and others. The remainder of this chapter focuses on