Cisco 7604 Configuration Manual page 850

Understanding NetFlow
Flow Mask Conflicts
Several features use the NetFlow table.
Table 50-1 Feature Requirements for Flow Masks
Feature
Reflexive ACL
TCP Intercept
Context Based Access Control (CBAC)
Web Cache Redirect (WCCP)
Server Load Balancing (SLB)
Network Address Translation (NAT)
NetFlow Data Export (NDE)
Sampled NetFlow
NetFlow Aggregation
Microflow Policing
Because of the variety of feature requirements, potential flow mask conflicts can occur. Note the
following flow mask constraints:
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The Feature Manager software in the MSFC is responsible for resolving feature conflicts. The Feature
Manager's main strategy is to select a common flow mask that satisfies all the configured NetFlow
features.
However, the Feature Manager may not find a common flow mask for the configured features, because
some features have very specific requirements for the flow mask. To resolve the feature conflict, Feature
Manager software may direct one of the features to be processed in software on the MSFC.
In the extreme case, Feature Manager software gives priority to the feature that is configured first and
rejects configuration requests for subsequent features. When you attempt to configure a subsequent
feature that the Feature Manager cannot accommodate, you receive a failure message at the CLI.
Follow these guidelines to avoid problems with feature conflicts:
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With a PFC2, all features share the same global flow mask.
With a PFC3, all features must share the same limited set of flow masks.
The PFC can apply only one flow mask to each packet lookup.
Configure your highest priority features first. If an unresolvable conflict occurs, your lower priority
features may be blocked.
If possible, configure features only on the interfaces where the feature is required.
Pay attention to response messages. If the Feature Manager turns off hardware assist for a feature,
you need to ensure that feature processing does not overload the RP processor.
Table 50-1 lists the flow mask requirements for each feature.
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Chapter 50 Configuring NetFlow
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