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Cisco ASA Series Firewall ASDM Configuration Guide
Chapter 31 Configuring the ASA IPS Module
Information About the ASA IPS Module
Operating Modes
You can send traffic to the ASA IPS module using one of the following modes:
• Inline mode—This mode places the ASA IPS module directly in the traffic flow (see Figure 31-1).
No traffic that you identified for IPS inspection can continue through the ASA without first passing
through, and being inspected by, the ASA IPS module. This mode is the most secure because every
packet that you identify for inspection is analyzed before being allowed through. Also, the ASA IPS
module can implement a blocking policy on a packet-by-packet basis. This mode, however, can
affect throughput.
• Promiscuous mode—This mode sends a duplicate stream of traffic to the ASA IPS module. This
mode is less secure, but has little impact on traffic throughput. Unlike inline mode, in promiscuous
mode the ASA IPS module can only block traffic by instructing the ASA to shun the traffic or by
resetting a connection on the ASA. Also, while the ASA IPS module is analyzing the traffic, a small
amount of traffic might pass through the ASA before the ASA IPS module can shun it. Figure 31-2
shows the ASA IPS module in promiscuous mode. In this example, the ASA IPS module sends a
shun message to the ASA for traffic it identified as a threat.
Figure 31-2 ASA IPS module Traffic Flow in the ASA: Promiscuous Mode
Using Virtual Sensors (ASA 5510 and Higher)
The ASA IPS module running IPS software Version 6.0 and later can run multiple virtual sensors, which
means you can configure multiple security policies on the ASA IPS module. You can assign each ASA
security context or single mode ASA to one or more virtual sensors, or you can assign multiple security
contexts to the same virtual sensor. See the IPS documentation for more information about virtual
sensors, including the maximum number of sensors supported.
Figure 31-3 shows one security context paired with one virtual sensor (in inline mode), while two
security contexts share the same virtual sensor.
ASA
Main System
inside
IPS
IPS inspection
outside
VPN
Decryption
Firewall
Policy
Shun
message
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