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Catalyst 6500 Series Switch and Cisco 7600 Series Router Firewall Services Module Configuration Guide
OL-6392-01
Chapter 4 Configuring the Firewall Mode
Firewall Mode Overview
Figure 4-5 Outside to Inside
The steps below describe how data moves through the FWSM (see Figure 4-5):
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 FWSM receives the packet, and because it is a new session, the FWSM verifies if the packet is
allowed according to the security policy (ACLs, filters, AAA).
3. The packet is denied, and the FWSM drops the packet and logs the connection attempt.
If the outside user is attempting to attack the inside network, the FWSM employs many technologies
to determine if a packet is valid for an already established session. See the “Other Protection
Features” section on page 1-6 for more information.
www.cisco.com
User
10.1.2.27
FWSM
Outside
Inside DMZ
Switch
209.165.201.2
10.1.1.110.1.2.1
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