ccna 3 book

ccna 3 book.1 indicates that the ACL is a standard ACL list.The deny parameter specifies that traffic matching the selected parameter is no longer forwarded. 172.16.4.0 IP address of the source subnet. 0.0.0.255 is the wildcard mask. Bits indicate that a match must be made when performing an operation with; 1 bit indicates that it can be ignored. The first three 8-bitThe first 3 8-bit groups have a mask of 0, indicating that these bits must match. A mask of 255 for the last 8-bit group indicates that it can be ignored.The permit parameter specifies that traffic matching the selected parameter will be forwarded.84 Chapter 4 Implementing Firewall TechnologiesThe any parameter is an abbreviation for the source IP address. It indicates that the source address is 0.0.0.0, the wildcard mask is 255.255.255.255, and all source addresses match. Since there is an implicit deny statement at the end of all ACLs, the following command, access-list1permitany, should be included to ensure that only traffic from 172.16.4.0 is blocked and other traffic is let through.4.1.1.7 Extended ACL ExampleCompared to standard ACLs, extended ACLs can deny or allow specific types of traffic. Consider a scenario where FTP traffic from one subnet must be denied access to another subnet. In this example, the extended ACL is needed because specific types of traffic need to be filtered.R1(config)# access-list 101 denytcp 172.16.4.0 0.0.0.255 172.16.3.0 0.0.0.255 eq 21 R1(config)# access-list 101 denytcp 172.16.4.0 0.0.0.255 172.16.3.0 0.0.0.0.255 eq 20 R1(config)# access-list 101 permit ip anyanyIn this ACL, FTP access from subnet 172.16.4.0/24 to subnet 172.16.3.0/24 is denied and all other traffic is allowed