Adaptive Security Algorithm

By default, all traffic that goes through the ASA is inspected using the Adaptive Security Algorithm and is either allowed through or dropped based on the security policy. The ASA maximizes the firewall performance by checking the state of each packet (is this a new connection or an established connection?) and assigning it to either the session management path (a new connection SYN packet), the fast path (an established connection), or the control plane path (advanced inspection). 

References

- Information about TCP State Bypass

- ASA Firewall Mode Overview

- Stateful Inspection Overview

 

ASA Basic Firewall Config

Step1
ASA(config)# enable password mysecretpassword

Step2
ASA(config)# username admin password Pa55w0rd
! use this LOCAL username to authenticate for SSH connections
ASA(config)#  aaa authentication ssh console LOCAL
ASA(config)# crypto key generate rsa modulus 1024

! Specify the hosts allowed to connect to the security appliance.
ASA(config)# ssh 10.1.1.1 255.255.255.255 inside
ASA(config)# ssh 200.200.200.1 255.255.255.255 outside

Step3
ASA(config)# int Gi0/1
ASA(config-if)# nameif inside
ASA(config-if)# ip add 10.0.0.1 255.255.255.0
ASA(config-if)# security-level 100
ASA(config-if)# no shut

ASA(config)# int Gi0/0
ASA(config-if)# nameif outside
ASA(config-if)# ip add 200.0.0.1 255.255.255.0
ASA(config-if)# security-level 0
ASA(config-if)# no shut

Step4
! default route to the internet
ASA(config)# route outside 0.0.0.0 0.0.0.0 100.1.1.1
! route to internal network
ASA(config)# route inside 192.168.1.0 255.255.255.0 192.168.1.1

ASA at-a-glance

I just started to explore about ASA, as I needed to implement a cisco firewall for one of my projects. Fortunately, Narbik also launched Site-to-Site VPN which is sample part of his CCIE Security Workbook. I would advocate that his book is incredibly awesome because of the way he explains and the topology he designs for the labs.

Furthermore, I recommend to check the ASA specifications and models comparison at the Cisco website. It will be useful for pre-sales engineers.

0x41 & 0x1

For Cisco ASA Password Recovery, just memorize 0x41 & 0x1. Simply Enough!

rommon #1>confreg 0x41,
which tells the appliance to ignore its saved (startup) configuration upon boot.

asa(config)#config-register 0x01
While still in Configuration Mode, reset the configuration register to the default of 0x01 to force the security appliance to read its startup configuration on boot.