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Software Configuration Guide—Release 12.2(25)SG
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Chapter38 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 hence 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 enables 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 will be NULL. If the traffic is being switched
on a VLAN that is associated with an SVI, the input and output interface information will point to
the same Layer 3 interface.
•Switched flows are exported according to regular export configurations; a sep arate export CLI does
not exist.
•In the main cache, switched IP flows and routed IP flows are indistinguishable; this is due to a
hardware limitation.
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. (See “Configuring User Based Rate Limiting” on page36.)
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.
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
Step1 Switch# conf terminal Enter configuration mode.
Step2 Switch(config)# ip flow ingress Enable routed flow collection.
Step3 Switch(config)# ip flow ingress
layer2-switched
Enable switched flow collection.