Cisco ASA: ACL

Technology: FIREWALLS

Area: Traffic restrictions

Vendor: CISCO

Software: CISCO ADAPTIVE SECURITY APPLIANCE (ASA), ASA-OS, 8.3+

Platform: CISCO ASA 5500, 5500-X

ACL in ASA is similar to router configuration, except for processing and mask definition (where the router uses wildcards). The adaptive security algorithm inspects only the first packet belonging to a particular session. Consecutive packets are “known” to ASA and are switched to “Fast Path” to not utilize ASA resources. ACLs are used to restrict or to permit traffic when there is a need to have transmission initiated from the lower to higher security level interface. There is only one ACL on one interface in particular direction permission.

To configure ACL to allow connection to host 172.16.1.2 use the command below:

access-list outside_in extended permit ip any host 172.16.1.2
access-group outside_in in interface outside

Note: in ASA-OS versions after 8.3 when using NAT, there is a rule to pointing the real destination address, in our case 172.16.1.2 instead of mapped IP like in older versions

Useful verification commands:

ASA2# show run access-list
ASA2# show access-list