How to Create and Manage Access - Control Lists on Cisco ASA and PIX Firewalls

April 5, 2010 - PRLog -- Access Control Lists (ACLs) are sequential lists of permit and deny conditions applied to traffic flows on a device interface. ACLs are based on various criteria including protocol type source IP address, destination IP address, source port number, and/or destination port number.

ACLs can be used to filter traffic for various purposes including security, monitoring, route selection, and network address translation. ACLs are comprised of one or more Access Control Entries (ACEs). Each ACE is an individual line within an ACL.

ACLs on a Cisco ASA Security Appliance (or a PIX firewall running software version 7.x or later) are similar to those on a Cisco router, but not identical. Firewalls use real subnet masks instead of the inverted mask used on a router. ACLs on a firewall are always named instead of numbered and are assumed to be an extended list.

The syntax of an ACE is relatively straight-forward:

Ciscoasa(config)#access-list name [line number] [extended] {permit | deny} protocol
source_IP_address source_netmask [operator source_port] destination_IP_address
destination_netmask [operator destination_port] [log [[disable | default] | [level]] [interval seconds]] [time-range name] [inactive]

Here's an example:

asa(config)# access-list demo1 permit tcp 10.1.0.0 255.255.255.0 any eq www
asa(config)# access-list demo1 permit tcp 10.1.0.0 255.255.255.0 any eq 443
asa(config)# show access-list demo1
access-list demo1; 2 elements
access-list demo1 line 1 extended permit tcp 10.1.0.0 255.255.255.0 any eq www
access-list demo1 line 2 extended permit tcp 10.1.0.0 255.255.255.0 any eq https

In the above example, an ACL called "demo1" is created in which the first ACE permits TCP traffic originating on the 10.1.0.0 subnet to go to any destination IP address with the destination port of 80 (www). In the second ACE, the same traffic flow is permitted for destination port 443. Notice in the output of the show access-list that line numbers are displayed and the extended parameter is also included, even though neither was included in the configuration statements.

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