Access lists can even be used in situations that don’t necessarily involve blocking packets. For
example, you can use them to control which networks will or won’t be advertised by dynamic
routing protocols. How you configure the access list is the same. The difference here is simply
how you apply it—to a routing protocol instead of an interface. When you apply an access list in
this way, it’s called a distribute list, and it doesn’t stop routing advertisements, it just controls
their content. You can also use access lists to categorize packets for queuing or QoS-type
services and for controlling which types of traffic can activate a pricey ISDN link.