Dynamic, or "lock-and-key," access lists are one of the IOS features commonly used to tighten security on a router.
They allow the network administrator to grant temporary access to a network or service when a user gives a valid ID
and password. Dynamic access list statements have several advantages over static ACL entries: access can be
granted for only a short time, and access can be based on the user, rather than on the IP address of the workstation.