cisco ccna 200-301 en espa?ol pdf

cisco ccna 200-301 en espa?ol pdf.1. Allow traffic from subnet 172.16.0.0/16 to pass.2. prohibit passage from host 172.16.1.1/32.As mentioned earlier, the router processes these statements in top-to-bottom order. Suppose a packet with a source IP address of 172.16.1.1 is received at the router. Given the aforementioned ACL, the router compares the packet with the first statement. Does the source address of the packet belong to network 172.16.0.0/16? Yes. Therefore the comparison indicates that the router should allow the packet to pass. Note that after the router finds that the packet matches the first statement, it does not process the second statement. In this example, all traffic from subnet 172.16.0.0/16 will be allowed through, even if the traffic comes from host 172.16.1.1.Here are the two statements in reverse order in the ACL to see how this will affect the traffic1. prohibit traffic from host 172.16.1.1 from passing through.2. allow traffic from subnet 172.16.0.0/16 to pass.If traffic sent by 172.16.1.1 passes through the router, the IOS will first compare these packets with the first ACL statement. Since the source address is 172.16.1.1, the router discards these packets and does not process the other statements in the ACL. In this example, whatever traffic is sent from 172.16.1.1 is discarded. If another device (such as 172.16.1.2) sends traffic through this router, the router will compare the packet to the first ACL statement. Since the source address of the packet does not match the source address in that ACL statement, the router then processes the next statement: the contents of the packet are compared to this statement and a match is found. The router therefore takes the specified action and allows traffic from 172.16.1.2 to pass. As you can see from these two ACL examples, the order of the statements in the ACL is very important and affects which traffic is allowed through and which traffic is prohibited.It is important to be able to adjust the order of the statements in the ACL based on the desired outcome.Implicit deny statementAnother important aspect of top-down processing is that if the router compares the packet with each statement in the ACL and still does not find a match, it will discard the packet. This is referred to as implicit rejection. At the end of each ACL, there is an invisible statement that drops traffic that does not match any statement in the ACL. With this in mind, it makes no sense to create ACLs that contain only deny statements, because an implicit deny statement would then drop all traffic. Therefore, every ACL should contain at least one permit statement; otherwise it will discard all traffic because the statements in it are all deny statements (including hidden implicit deny statements).