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Software Configuration Guide—Release 15.0(2)SG
OL-23818-01
Chapter 56 Configuring NetFlow
Configuring NetFlow Statistics Collection
Mod Submodule Model Serial No. Hw Status
----+-----------------------+-----------------+------------+----+---------
1 Netflow Services Card WS-F4531 JAB062209CG 0.2 Ok
2 Netflow Services Card WS-F4531 JAB062209AG 0.2 Ok
Switch#
Note Enabling this feature does not impact the hardware-forwarding performance of the switch.
The effective size of the hardware flow cache table is 65,000 flows. (The hardware flow cache for the
Supervisor Engine V-10GE is 85,000 flows.) If more than 85,000 flows are active simultaneously,
statistics may be lost for some of the flows.
The effective size of the software flow table is 256, 000 flows. The NetFlow software manages the
consistency between the hardware and software tables, keeping the hardware table open by purging
inactive hardware flows to the software table.
User-configured timeout settings dictate when the flows are purged and exported through NDE from the
software cache. Hardware flow management ensures consistency between hardware flow purging and the
user-configured timeout settings.
Software-forwarded flows are also monitored. Moreover, statistics overflow if any flow receives traffic
at a sustained rate exceeding 2 gigabits per second. Generally, this situation should not occur because a
port cannot transmit at a rate higher than 1 gigabit per second.
Note By design, even if the timeout settings are high, flows automatically “age out” as they approach their
statistics limit.
Note First and last-seen (start and end times) flow timestamp accuracy is within 3 seconds.
Enabling NetFlow Statistics Collection
Note NetFlow Flow Statistics are disabled by default.
To enable NetFlow switching, first configure the switch for IP routing as described in the IP
configuration chapters in the Cisco IOS IP and IP Routing Configuration Guide. After you configure IP
routing, perform one of these tasks:
Command Purpose
Switch(config)# ip flow ingress
Enables NetFlow for IP routing.
Switch(config)# ip flow ingress
infer-fields
Enables NetFlow with inferred input/output
interfaces and source/destination BGP as
information.
The inter-fields option must be configured for AS
information to be determined.