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Software Configuration Guide—Release 15.0(2)SG
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Chapter 56 Configuring NetFlow
Configuring NetFlow Statistics Collection
Configuring Switched/Bridged IP Flows
NetFlow is defined as a collection of routed IP flows created and tracked for all routed IP traffic. In
switching environments, considerable IP traffic is switched within a VLAN and is not routed. This traffic
is termed switched/bridged IP traffic; the associated flow is termed switched/bridged IP flows. NetFlow
hardware is capable of creating and tracking this type of flow. The NetFlow Switched IP Flows feature
allows you to create, track, and export switched IP flows (that is, it creates and tracks flows for IP traffic
that is being switched and not routed).
Be aware of the following:
Switched IP flow collection cannot be enabled in isolation on Catalyst 4500 series switches. You
need to enable both routed flow and switched flow collection to start collecting switched IP flows.
Generally, the input and output interface information are NULL. If the traffic is being switched on
a VLAN that is associated with an SVI, the input and output interface information points to the same
Layer 3 interface.
Switched flows are exported according to regular export configurations; a separate export CLI does
not exist.
In the main cache, because of a hardware limitation, IP flows and routed IP flows are
indistinguishable.
Note To enable switched IP flow collection on all interfaces, you need to enter both the ip flow ingress and
ip flow ingress layer2-switched commands.
Note To enable a user-based rate limiting policy on the switched IP flow traffic, you need to enter the
ip flow ingress layer2-switched command, but not the ip flow ingress command. See “Configuring
User-Based Rate-Limiting” on page 37.
To configure the NetFlow cache and enable switched IP flow collection, perform this task:
This example shows how to display the contents of an IP flow cache that contains switch IP flows:
Switch# show ip cache flow
IP Flow Switching Cache, 17826816 bytes
2 active, 262142 inactive, 2 added
6 ager polls, 0 flow alloc failures
Active flows timeout in 30 minutes
Inactive flows timeout in 15 seconds
IP Sub Flow Cache, 1081480 bytes
2 active, 65534 inactive, 2 added, 2 added to flow
0 alloc failures, 0 force free
1 chunk, 1 chunk added
last clearing of statistics never
Command Purpose
Step 1 Switch# conf terminal Enters configuration mode.
Step 2 Switch(config)# ip flow ingress Enables routed flow collection.
Step 3 Switch(config)# ip flow ingress
layer2-switched Enables switched flow collection.