Cisco 2950 Software Configuration Guide - Page 547
Creating Named Standard and Extended ACLs
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Chapter 29 Configuring Network Security with ACLs Configuring ACLs Use the no access-list access-list-number global configuration command to delete the entire access list. You cannot delete individual ACEs from numbered access lists. This example shows how to create and display an extended access list to deny Telnet access from any host in network 171.69.198.0 to any host in network 172.20.52.0 and permit any others. (The eq keyword after the destination address means to test for the TCP destination port number equaling Telnet.) Switch(config)# access-list 102 deny tcp 171.69.198.0 0.0.0.255 172.20.52.0 0.0.0.255 eq telnet Switch(config)# access-list 102 permit tcp any any Switch(config)# end Switch# show access-lists Extended IP access list 102 deny tcp 171.69.198.0 0.0.0.255 172.20.52.0 0.0.0.255 eq telnet permit tcp any any After an ACL is created, any additions (possibly entered from the terminal) are placed at the end of the list. You can add ACEs to an ACL, but deleting any ACE deletes the entire ACL. Note When creating an ACL, remember that, by default, the end of the access list contains an implicit deny statement for all packets if the access list does not find a match before reaching the end. With standard access lists, if you omit the mask from an associated IP host address ACL specification, 0.0.0.0 is assumed to be the mask. After creating an ACL, you must apply it to a line or interface, as described in the "Applying ACLs to Terminal Lines or Physical Interfaces" section on page 29-19. Creating Named Standard and Extended ACLs You can identify IP ACLs with an alphanumeric string (a name) rather than a number. You can use named ACLs to configure more IP access lists on a switch than if you use numbered access lists. If you identify your access list with a name rather than a number, the mode and command syntax are slightly different. However, not all commands that use IP access lists accept a named ACL. Note The name you give to a standard ACL or extended ACL can also be a number in the supported range of access list numbers. That is, the name of a standard IP ACL can be 1 to 99; the name of an extended IP ACL can be 100 to 199. The advantage of using named ACLs instead of numbered lists is that you can delete individual entries from a named list. Consider these guidelines and limitations before configuring named ACLs: • A standard ACL and an extended ACL cannot have the same name. • Numbered ACLs are also available, as described in the "Creating Standard and Extended IP ACLs" section on page 29-7. 78-11380-10 Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide 29-13
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