I've got the following question from Matthew: »how would one go about matching the default route for filtering using standard ACLs?«
In all routing protocols but EIGRP (which can carry the »default candidate« flag on any IP prefix), the default route has IP address 0.0.0.0 and subnet mask 0.0.0.0.
To match the default route with a standard ACL, use access-list x permit 0.0.0.0. To match it with an extended ACL (which matches the IP address and the subnet mask portions), you have to use access-list y permit ip host 0.0.0.0 host 0.0.0.0. And finally, to match the default route in a prefix list, use ip prefix-list z permit 0.0.0.0/0.