CHAPTE R
9-1
Cisco ASA Series Firewall CLI Configuration Guide
9
Getting Started with Application Layer Protocol Inspection
This chapter describes how to configure application layer protocol inspection. Inspection engines are
required for services that embed IP addressing information in the user data packet or that open secondary
channels on dynamically assigned ports. These protocols require the ASA to do a deep packet inspection
instead of passing the packet through the fast path (see the general operations configuration guide for
more information about the fast path). As a result, inspection engines can affect overall throughput.
Several common inspection engines are enabled on the ASA by default, but you might need to enable
others depending on your network.
This chapter includes the following sections:
Information about Application Layer Protocol Inspection, page9-1
Guidelines and Limitations, page9-3
Default Settings and NAT Limitations, page9-4
Configuring Application Layer Protocol Inspection, page9-7

Information about Application Layer Protocol Inspection

This section includes the following topics:
How Inspection Engines Work, page9-1
When to Use Application Protocol Inspection, page 9-2

How Inspection Engines Work

As illustrated in Figure 9-1, the ASA uses three databases for its basic operation:
ACLs—Used for authentication and authorization of connections based on specific networks, hosts,
and services (TCP/UDP port numbers).
Inspections—Contains a static, predefined set of application-level inspection functions.
Connections (XLATE and CONN tables)—Maintains state and other information about each
established connection. This information is used by the Adaptive Security Algorithm and
cut-through proxy to efficiently forward traffic within established sessions.