| 3.2 |  | Types of IP ACLs |
| 3.2.1 |  | Standard ACLs |

| A number of different ACL types are available to filter traffic. Figure lists the different types of access lists and Figure provides the standard for numbering access lists based on their types. Standard ACLs are the oldest type of ACL. Standard ACLs control traffic by comparing the source address of the IP packets to the addresses configured in the ACL. Figure shows the command syntax format of a standard ACL.

In all software releases, the access-list number can be number from 1 to 99. In Cisco IOS Software Release 12.0.1, standard ACLs began using additional numbers, from 1300 to 1999. These additional numbers are referred to as expanded IP ACLs. Cisco IOS Software Release 11.2 added the ability to use list name in standard ACLs.

In early software releases, outbound was the default when a keyword "out" or "in" was not specified. The direction must be specified in later software releases . Remember, a source/source-wildcard setting of 0.0.0.0 255.255.255.255 can also be written as any. The wildcard can be omitted if it is all zeros. Therefore, 10.1.1.2 0.0.0.0 is the same as host 10.1.1.2.

An example of using a standard ACL to block all traffic except that from source 10.1.1.x is shown in Figure .

Figure shows an example in which a standard access list is created and applied to the incoming Internet traffic interface. The access list denies all inbound traffic from the Internet that contains a source address from known reserved RFC 1918 addresses and permits any other traffic from the Internet to the corporate campus.