Using Flexible NetFlow Flow Sampling Last Updated: October 31, 2011

Using Flexible NetFlow Flow Sampling Last Updated: October 31, 2011
Using Flexible NetFlow Flow Sampling
Last Updated: October 31, 2011
This document contains information about and instructions for configuring sampling to reduce the CPU
overhead of analyzing traffic with Flexible NetFlow.
NetFlow is a Cisco IOS technology that provides statistics on packets flowing through a router. NetFlow is
the standard for acquiring IP operational data from IP networks. NetFlow provides data to support network
and security monitoring, network planning, traffic analysis, and IP accounting.
Flexible NetFlow improves on original NetFlow by adding the capability to customize the traffic analysis
parameters for your specific requirements. Flexible NetFlow faciltates the creation of more complex
configurations for traffic analysis and data export through the use of reusable configuration components.
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Finding Feature Information, page 1
Prerequisites for Using Flow Sampling, page 2
Restrictions for Using Flow Sampling, page 2
Information About Flexible NetFlow Samplers, page 2
How to Configure Flexible NetFlow Flow Sampling, page 3
Configuration Examples for Using Flexible NetFlow Flow Sampling, page 7
Where to Go Next, page 9
Additional References, page 9
Feature Information for Flexible NetFlow, page 10
Finding Feature Information
Your software release may not support all the features documented in this module. For the latest feature
information and caveats, see the release notes for your platform and software release. To find information
about the features documented in this module, and to see a list of the releases in which each feature is
supported, see the Feature Information Table at the end of this document.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support.
To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Americas Headquarters:
Cisco Systems, Inc., 170 West Tasman Drive, San Jose, CA 95134-1706 USA
Flow Samplers
Prerequisites for Using Flow Sampling
Prerequisites for Using Flow Sampling
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You are familiar with the information in the " Cisco IOS Flexible NetFlow Overview " module.
The networking device must be running a Cisco IOS release that supports Flexible NetFlow.
IPv4 Traffic
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The networking device must be configured for IPv4 routing.
One of the following must be enabled on your router and on any interfaces on which you want to
enable Flexible NetFlow: Cisco Express Forwarding or distributed Cisco Express Forwarding.
IPv6 Traffic
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The networking device must be configured for IPv6 routing.
One of the following must be enabled on your router and on any interfaces on which you want to
enable Flexible NetFlow: Cisco Express Forwarding IPv6 or distributed Cisco Express Forwarding
IPv6.
Restrictions for Using Flow Sampling
Cisco IOS Release 12.2(50)SY
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Deterministic sampling is not supported.
Information About Flexible NetFlow Samplers
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Flow Samplers, page 2
Flow Samplers
Flow samplers are created as separate components in a router’s configuration. Flow samplers are used to
reduce the load on the device that is running Flexible NetFlow by limiting the number of packets that are
selected for analysis. Samplers use either random or deterministic sampling techniques (modes):
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Deterministic--The same sampling position is used each time a sample is taken.
Random--A randomly selected sampling position is used each time a sample is taken.
Flow sampling exchanges monitoring accuracy for router performance. When you apply a sampler to a
flow monitor, the overhead load on the router of running the flow monitor is reduced because the number
of packets that the flow monitor must analyze is reduced. The reduction in the number of packets that are
analyzed by the flow monitor causes a corresponding reduction in the accuracy of the information stored in
the flow monitor’s cache.
Samplers are combined with flow monitors when they are applied to an interface with the ip flow monitor
command.
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Configuring a Flow Monitor
How to Configure Flexible NetFlow Flow Sampling
How to Configure Flexible NetFlow Flow Sampling
Flow sampling reduces the CPU overhead of analyzing traffic with Flexible NetFlow by reducing the
number of packets that are analyzed.
Note
Only the keywords and arguments required for the Flexible NetFlow commands used in these tasks are
explained in these tasks. For information about the other keywords and arguments available for these
Flexible NetFlow commands, refer to the Cisco IOS Flexible NetFlow Command Reference .
•
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Configuring a Flow Monitor, page 3
Configuring and Enabling Flow Sampling, page 4
Configuring a Flow Monitor
Samplers are applied to an interface in conjunction with a flow monitor. You must create a flow monitor to
configure the types of traffic that you want to analyze before you can enable sampling. To configure a flow
monitor, perform the following required task.
Each flow monitor has a separate cache assigned to it. Each flow monitor requires a record to define the
contents and layout of its cache entries. The record format can be one of the predefined record formats, or
an advanced user may create his or her own record format using the collect and matchcommands in
Flexible NetFlow flow record configuration mode.
Note
You must use the no ip flow monitorcommand to remove a flow monitor from all of the interfaces to
which you have applied it before you can modify the parameters for the record command on the flow
monitor.
SUMMARY STEPS
1. enable
2. configure terminal
3. flow monitor monitor-name
4. description description
5. record {record-name | netflow-original | netflow {ipv4 | ipv6} record [peer]}
6. end
3
Configuring and Enabling Flow Sampling
How to Configure Flexible NetFlow Flow Sampling
DETAILED STEPS
Command or Action
Step 1 enable
Purpose
Enables privileged EXEC mode.
•
Enter your password if prompted.
Example:
Router> enable
Step 2 configure terminal
Enters global configuration mode.
Example:
Router# configure terminal
Step 3 flow monitor monitor-name
Creates a flow monitor and enters Flexible NetFlow
flow monitor configuration mode.
•
Example:
This command also allows you to modify an
existing flow monitor.
Router(config)# flow monitor FLOW-MONITOR-1
Step 4 description description
(Optional) Creates a description for the flow monitor.
Example:
Router(config-flow-monitor)# description Used for
basic traffic analysis
Step 5 record {record-name | netflow-original | netflow {ipv4 | ipv6} Specifies the record for the flow monitor.
record [peer]}
Example:
Router(config-flow-monitor)# record netflow ipv4
original-input
Step 6 end
Exits Flexible NetFlow flow monitor configuration
mode and returns to privileged EXEC mode.
Example:
Router(config-flow-monitor)# end
Configuring and Enabling Flow Sampling
To configure and enable a flow sampler, perform the following required task.
4
Configuring and Enabling Flow Sampling
How to Configure Flexible NetFlow Flow Sampling
Note
When you specify the "NetFlow original," or the "NetFlow IPv4 original input," or the "NetFlow IPv6
original input" predefined record for the flow monitor to emulate original NetFlow, the flow monitor can be
used only for analyzing input (ingress) traffic.
When you specify the "NetFlow IPv4 original output" or the "NetFlow IPv6 original output" predefined
record for the flow monitor to emulate the Egress NetFlow Accounting feature, the flow monitor can be
used only for analyzing output (egress) traffic.
SUMMARY STEPS
1. enable
2. configure terminal
3. sampler sampler-name
4. description description
5. mode {deterministic | random} 1 out-of window-size
6. exit
7. interface type number
8. {ip | ipv6} flow monitor monitor-name [[sampler] sampler-name] {input | output}
9. end
10. show sampler sampler-name
DETAILED STEPS
Command or Action
Step 1 enable
Purpose
Enables privileged EXEC mode.
•
Enter your password if prompted.
Example:
Router> enable
Step 2 configure terminal
Enters global configuration mode.
Example:
Router# configure terminal
Step 3 sampler sampler-name
Creates a sampler and enters sampler configuration mode.
•
Example:
This command also allows you to modify an existing
sampler.
Router(config)# sampler SAMPLER-1
5
Configuring and Enabling Flow Sampling
How to Configure Flexible NetFlow Flow Sampling
Command or Action
Step 4 description description
Purpose
(Optional) Creates a description for the flow sampler.
Example:
Router(config-sampler)# description Sample at 50%
Step 5 mode {deterministic | random} 1 out-of window-size
Example:
Specifies the sampler mode and the flow sampler window
size.
•
The range for the window-size argument is from 2 to
32,768.
Router(config-sampler)# mode random 1 out-of 2
Step 6 exit
Exits sampler configuration mode and returns to global
configuration mode.
Example:
Router(config-sampler)# exit
Step 7 interface type number
Specifies an interface and enters interface configuration
mode.
Example:
Router(config)# interface ethernet 0/0
Step 8 {ip | ipv6} flow monitor monitor-name [[sampler]
sampler-name] {input | output}
Assigns the flow monitor and the flow sampler that you
created to the interface to enable sampling.
Example:
Router(config-if)# ip flow monitor FLOW-MONITOR-1
sampler SAMPLER-1 input
Step 9 end
Exits interface configuration mode and returns to
privileged EXEC mode.
Example:
Router(config-if)# end
Step 10 show sampler sampler-name
Example:
Router# dhoe sampler SAMPLER-1
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Displays the status and statistics of the flow sampler that
you configured and enabled,.
Example Configuring and Enabling a Deterministic Sampler for IPv4 Traffic
Configuration Examples for Using Flexible NetFlow Flow Sampling
Configuration Examples for Using Flexible NetFlow Flow
Sampling
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Example Configuring and Enabling a Deterministic Sampler for IPv4 Traffic, page 7
Example Configuring and Enabling a Deterministic Sampler for IPv6 Traffic, page 7
Example Adding a Sampler to a Flow Monitor When a Flow Monitor Is Already Enabled, page 8
Example Removing a Sampler from a Flow Monitor, page 8
Example Configuring and Enabling a Deterministic Sampler for IPv4 Traffic
The following example shows how to configure and enable deterministic sampling for IPv4 output traffic.
This sample starts in global configuration mode:
!
flow monitor FLOW-MONITOR-1
record netflow ipv4 original-output
exit
!
sampler SAMPLER-1
mode deterministic 1 out-of 2
exit
!
ip cef
!
interface Ethernet 0/0
ip address 172.16.6.2 255.255.255.0
ip flow monitor FLOW-MONITOR-1 sampler SAMPLER-1 output
!
The following example shows how to configure and enable deterministic sampling for IPv4 input traffic.
This sample starts in global configuration mode:
!
flow monitor FLOW-MONITOR-1
record netflow ipv4 original-input
exit
!
sampler SAMPLER-1
mode deterministic 1 out-of 2
exit
!
ip cef
!
interface Ethernet 0/0
ip address 172.16.6.2 255.255.255.0
ip flow monitor FLOW-MONITOR-1 sampler SAMPLER-1 input
!
Example Configuring and Enabling a Deterministic Sampler for IPv6 Traffic
The following example shows how to configure and enable deterministic sampling for IPv6 output traffic.
This sample starts in global configuration mode:
!
flow monitor FLOW-MONITOR-2
record netflow ipv6 original-output
exit
7
Example Adding a Sampler to a Flow Monitor When a Flow Monitor Is Already Enabled
Configuration Examples for Using Flexible NetFlow Flow Sampling
!
sampler SAMPLER-1
mode deterministic 1 out-of 2
exit
!
ip cef
ipv6 cef
!
interface Ethernet 0/0
ipv6 address 2001:DB8:2:ABCD::2/48
ipv6 flow monitor FLOW-MONITOR-2 sampler SAMPLER-1 output
!
The following example shows how to configure and enable deterministic sampling for IPv6 input traffic.
This sample starts in global configuration mode:
!
flow monitor FLOW-MONITOR-2
record netflow ipv6 original-input
exit
!
sampler SAMPLER-1
mode deterministic 1 out-of 2
exit
!
ip cef
ipv6 cef
!
interface Ethernet 0/0
ipv6 address 2001:DB8:2:ABCD::2/48
ipv6 flow monitor FLOW-MONITOR-1 sampler SAMPLER-1 input
!
Example Adding a Sampler to a Flow Monitor When a Flow Monitor Is
Already Enabled
The following example shows what happens when you try to add a sampler to a flow monitor that has
already been enabled on an interface without a sampler:
Router(config)# interface Ethernet
0/0
Router(config-if)# ip flow monitor FLOW-MONITOR-1 sampler SAMPLER-2 input
% Flow Monitor: Flow Monitor 'FLOW-MONITOR-1' is already on in full mode and cannot be
enabled with a sampler.
The following example shows how to remove the flow monitor from the interface so that it can be enabled
with the sampler:
Router(config)# interface Ethernet
0/0
Router(config-if)# no ip flow monitor FLOW-MONITOR-1 input
Router(config-if)# ip flow monitor FLOW-MONITOR-1 sampler SAMPLER-2 input
Example Removing a Sampler from a Flow Monitor
The following example shows what happens when you try to remove a sampler from a flow monitor on an
interface by entering the flow monitor command again without the sampler keyword and argument:
Router(config)# interface Ethernet
0/0
Router(config-if)# ip flow monitor FLOW-MONITOR-1 input
% Flow Monitor: Flow Monitor 'FLOW-MONITOR-1' is already on in sampled mode and cannot be
enabled in full mode.
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Example Removing a Sampler from a Flow Monitor
Where to Go Next
The following example shows how to remove the flow monitor that was enabled with a sampler from the
interface so that it can be enabled without the sampler:
Router(config)# interface Ethernet
0/0
Router(config-if)# no ip flow monitor FLOW-MONITOR-1 sampler SAMPLER-2 input
Router(config-if)# ip flow monitor FLOW-MONITOR-1 input
Where to Go Next
For information on advanced Flexible NetFlow configurations for specific purposes such as quality of
service (QoS) and bandwidth monitoring, application and user flow monitoring and profiling, and security
analysis, refer to the "Customizing Cisco IOS Flexible NetFlow Flow Records and Flow Monitors"
module.
If you want to configure any of the predefined records for Flexible NetFlow, refer to the "Configuring
Cisco IOS Flexible NetFlow with Predefined Records" module.
If you want to configure data export for Flexible NetFlow, refer to the "Configuring Data Export for Cisco
IOS Flexible NetFlow with Flow Exporters" module.
Additional References
Related Documents
Related Topic
Document Title
Cisco IOS commands
Cisco IOS Master Commands List, All Releases
Overview of Flexible NetFlow
"Cisco IOS Flexible NetFlow Overview"
Emulating original NetFlow with Flexible NetFlow
"Getting Started with Configuring Cisco IOS
Flexible NetFlow"
Configuring flow exporters to export Flexible
NetFlow data
"Configuring Data Export for Cisco IOS Flexible
NetFlow with Flow Exporters"
Customizing Flexible NetFlow
"Customizing Cisco IOS Flexible NetFlow Flow
Records and Flow Monitors"
Configuring Flexible NetFlow using predefined
records
"Configuring Cisco IOS Flexible NetFlow with
Predefined Records"
Using Flexible NetFlow Top N Talkers to analyze
network traffic
"Using Cisco IOS Flexible NetFlow Top N Talkers
to Analyze Network Traffic"
Configuring IPv4 multicast statistics support for
Flexible NetFlow
"Configuring IPv4 Multicast Statistics Support for
Cisco IOS Flexible NetFlow"
Configuration commands for Flexible NetFlow
Cisco IOS Flexible NetFlow Command Reference
9
Example Removing a Sampler from a Flow Monitor
Feature Information for Flexible NetFlow
Standards
Standard
Title
None
--
MIBs
MIB
MIBs Link
None
To locate and download MIBs for selected
platforms, Cisco software releases, and feature sets,
use Cisco MIB Locator found at the following
URL:
http://www.cisco.com/go/mibs
RFCs
RFC
Title
RFC 3954
Cisco Systems NetFlow Services Export Version 9
Technical Assistance
Description
Link
The Cisco Support and Documentation website
provides online resources to download
documentation, software, and tools. Use these
resources to install and configure the software and
to troubleshoot and resolve technical issues with
Cisco products and technologies. Access to most
tools on the Cisco Support and Documentation
website requires a Cisco.com user ID and
password.
http://www.cisco.com/cisco/web/support/
index.html
Feature Information for Flexible NetFlow
The following table provides release information about the feature or features described in this module.
This table lists only the software release that introduced support for a given feature in a given software
release train. Unless noted otherwise, subsequent releases of that software release train also support that
feature.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support.
To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
10
Example Removing a Sampler from a Flow Monitor
Feature Information for Flexible NetFlow
Table 1
Feature Information for Flexible NetFlow
Feature Name
Releases
Feature Information
Flexible NetFlow
12.2(33)SRC
Flexible NetFlow is introduced.
12.2(50)SY
Support for this feature was
added for Cisco 7200 series
routers in Cisco IOS Release
12.2(33)SRC.
12.4(9)T
15.0(1)SY
The following commands were
introduced or modified: cache
(Flexible NetFlow), clear flow
exporter, clear flow monitor,
clear sampler, collect counter,
collect flow, collect interface,
collect ipv4, collect ipv4
destination, collect ipv4
fragmentation, collect ipv4
section, collect ipv4 source,
collect ipv4 total-length, collect
ipv4 ttl, collect routing, collect
timestamp sys-uptime, collect
transport, collect transport
icmp ipv4, collect transport tcp,
collect transport udp, debug
flow exporter, debug flow
monitor, debug flow record,
debug sampler, description
(Flexible NetFlow), destination,
dscp (Flexible NetFlow),
exporter, flow exporter, flow
monitor, flow record, ip flow
monitor, match flow, match
interface (Flexible NetFlow),
match ipv4, match ipv4
destination, match ipv4
fragmentation, match ipv4
section, match ipv4 source,
match ipv4 total-length, match
ipv4 ttl, match routing, match
transport, match transport
icmp ipv4, match transport tcp,
match transport udp, mode
(Flexible NetFlow), option
(Flexible NetFlow), record,
sampler, show flow exporter,
show flow interface, show flow
monitor, show flow record,
show sampler, source (Flexible
NetFlow), statistics packet,
11
Example Removing a Sampler from a Flow Monitor
Feature Name
Releases
Feature Information
template data timeout,
transport (Flexible NetFlow).
Flexible NetFlow--Random
Sampling
12.2(50)SY
12.4(20)T
15.0(1)SY
Flow samplers are created as
separate components in a router’s
configuration. Flow samplers are
used to reduce the load on the
device that is running Flexible
NetFlow by limiting the number
of packets that are selected for
analysis. Samplers use either
random or deterministic sampling
techniques (modes).
The following commands were
introduced or modified: clear
sampler, debug sampler, mode,
record, sampler show sampler.
Cisco and the Cisco logo are trademarks or registered trademarks of Cisco and/or its affiliates in the U.S.
and other countries. To view a list of Cisco trademarks, go to this URL: www.cisco.com/go/trademarks.
Third-party trademarks mentioned are the property of their respective owners. The use of the word partner
does not imply a partnership relationship between Cisco and any other company. (1110R)
Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be
actual addresses and phone numbers. Any examples, command display output, network topology diagrams,
and other figures included in the document are shown for illustrative purposes only. Any use of actual IP
addresses or phone numbers in illustrative content is unintentional and coincidental.
© 2011 Cisco Systems, Inc. All rights reserved.
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