Cisco ASA Series Cli Configuration Manual page 154

Firewall Mode Examples
Figure 1-6
The following steps describe how data moves through the ASA (see
1.
A user on the outside network attempts to reach an inside host (assuming the host has a routable
IP address).
If the inside network uses private addresses, no outside user can reach the inside network without
NAT. The outside user might attempt to reach an inside user by using an existing NAT session.
2.
The ASA receives the packet and because it is a new session, the ASA verifies if the packet is
allowed according to the security policy (access lists, filters, AAA).
3.
The packet is denied, and the ASA drops the packet and logs the connection attempt.
If the outside user is attempting to attack the inside network, the ASA employs many technologies
to determine if a packet is valid for an already established session.
Cisco ASA Series CLI Configuration Guide
1-18
Outside to Inside
www.example.com
Outside
209.165.201.2
10.1.2.1 10.1.1.1
Inside
User
10.1.2.27
Chapter 1 Configuring the Transparent or Routed Firewall
DMZ
Figure 1-6):