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cisco ccna 200-301 en espa?ol mega.On IOS devices, ACLs can be defined statically or downloaded dynamically from an authentication server. dynamic ACLs are typically applied when a user authenticates to the network (for example, through a switch port using IEEE 802.IX); after the user passes authentication, the switch downloads the ACL from the authentication server, applies it to the user's connected switch port and uses it to filter traffic. After the user leaves the network, the dynamic ACL is removed from the switch port. This book only describes how to configure static ACLs on IOS devices, and the usage and configuration of dynamic ACLs is beyond the scope of this book.Exam points Please keep in mind the filtering functions of the standard and extended ACLs listed in Table 21.1 and be able to describe the uses of dynamic ACLs.21.1.3 ProcessingACLs are basically statements that are grouped together using names or numbers. When processing packets against an ACL, the IOS takes specific steps to find matching statements in the ACL. The IOS processes ACLs in top-to-bottom order, first comparing the packet with the first statement and, if they match, taking the action specified in that statement: allow or deny.If the contents of the packet do not match the first ACL statement, the IOS proceeds to the next statement using the same process. If the second statement matches the contents of the packet, the IOS takes one of two actions. If it does not match, the IOS proceeds with the ACL until it finds a match. If the IOS does not find a matching ACL statement after processing the entire ACL, the packet is discarded. The following points are implicit in processing ACLs from top to bottom.. Once a matching statement is found, the ACL is not processed any further; . The order of the statements is important because after a match is found, the remaining statements are not processed any further; .. If no matching statement is found, the packet will be discarded.The order of the statementsOnce a match is found, no further statements are processed, so the order in which statements are listed in the ACL is very important. If there are two statements, one denying and one allowing traffic from the same host to pass, the first statement in line will be executed and the second statement in line will be ignored. Given that the order of the statements is critical, the more specific ACL statements should always be placed first, and the less specific statements should be placed second.To illustrate this point, look at an example. In this example, you have configured an ACL on your router that contains two statements in the following order.