ASA Packet Processing Post 8.3 Code
In this article, I will share my notes on the ASA packet process for version 8.3+. Domain 1.0 off the CCIE Security version blueprint focuses on perimeter security and intrusion prevention, both of which include the ASA. In order to understand the ASA and how it works, it is important to understand how packets are processed as they enter the ASA. The packet comes into the ingress interface and the ASA checks to see if there are any existing connections. If a connection already exists, ACL’s are bypassed and the packet is sent straight to the packet inspection, this is also known as the fast path. If a connection doesn’t currently exist then the packet needs to be checked against ACL’s for any matches, we can also see by looking at the diagram above, that the packet will be untranslated before it is matched against the ACL rules. If an ACL match is found and it is permitted, the packet will be inspected, likewise, if the packet is not permitted it is dropped. When a connection doe...