Using Flexible NetFlow Flow Sampling
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 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 facilitates the creation of more complex configurations for traffic analysis and data export through the use of reusable configuration components.
Finding Feature Information
Your software release may not support all the features documented in this module. For the latest caveats and feature information, see Bug Search Tool and 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.
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.
Prerequisites for Using Flexible NetFlow Flow Sampling
Restrictions for Using Flexible NetFlow Flow Sampling
Information About Flexible NetFlow Flow Sampling
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
by limiting the number of packets that
are selected for analysis.
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.
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 .
|
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. Perform this required task to configure a flow monitor.
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
match commands in Flexible NetFlow flow record configuration mode.
 Note |
You must use the
no
ip
flow
monitor command 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 STEPS1.
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
DETAILED STEPS | Command or Action | Purpose |
---|
Step 1 |
enable
Example:
|
Enables privileged EXEC mode.
|
Step 2 |
configure
terminal
Example:
Device# configure terminal
|
Enters global configuration mode.
|
Step 3 |
flow
monitor
monitor-name
Example:
Device(config)# flow monitor FLOW-MONITOR-1
|
Creates a flow monitor and enters Flexible NetFlow flow monitor configuration mode.
|
Step 4 |
description
description
Example:
Device(config-flow-monitor)# description Used for basic traffic analysis
|
(Optional) Creates a description for the flow monitor.
|
Step 5 |
record
{record-name |
netflow-original |
netflow {ipv4 |
ipv6}
record [peer]}
Example:
Device(config-flow-monitor)# record netflow ipv4 original-input
|
Specifies the record for the flow monitor.
|
Step 6 |
end
Example:
Device(config-flow-monitor)# end
|
Exits Flexible NetFlow flow monitor configuration mode and returns to privileged EXEC mode.
|
Perform this
required task to configure and enable a flow sampler.
SUMMARY STEPS1.
enable
2.
configure
terminal
3.
sampler
sampler-name
4.
description
description
5.
mode
{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 | Purpose |
---|
Step 1 |
enable
Example:
|
Enables
privileged EXEC mode.
|
Step 2 |
configure
terminal
Example:
Device# configure terminal
|
Enters global
configuration mode.
|
Step 3 |
sampler
sampler-name
Example:
Device(config)# sampler SAMPLER-1
|
Creates a
sampler and enters sampler configuration mode.
|
Step 4 |
description
description
Example:
Device(config-sampler)# description Sample at 50%
|
(Optional)
Creates a description for the flow sampler.
|
Step 5 |
mode
{random} 1
out-of
window-size
Example:
Device(config-sampler)# mode random 1 out-of 2
|
Specifies the sampler mode and the flow sampler window size.
|
Step 6 |
exit
Example:
Device(config-sampler)# exit
|
Exits sampler
configuration mode and returns to global configuration mode.
|
Step 7 |
interface
type
number
Example:
Device(config)# interface GigabitEthernet 0/0/0
|
Specifies an
interface and enters interface configuration mode.
|
Step 8 | {ip |
ipv6}
flow
monitor
monitor-name
[[sampler]
sampler-name]
{input |
output}
Example:
Device(config-if)# ip flow monitor FLOW-MONITOR-1 sampler SAMPLER-1 input
|
Assigns the
flow monitor and the flow sampler that you created to the interface to enable
sampling.
|
Step 9 |
end
Example:
|
Exits
interface configuration mode and returns to privileged EXEC mode.
|
Step 10 |
show
sampler
sampler-name
Example:
Device# show sampler SAMPLER-1
|
Displays the
status and statistics of the flow sampler that you configured and enabled.
|
Displaying the Status and Statistics of the Flow Sampler Configuration
To display the status and statistics of the flow sampler that you configured and enabled, perform the following optional task.
SUMMARY STEPS1.
enable
2.
show
sampler
sampler-name
DETAILED STEPS
Step 1
|
enable
The
enable command enters privileged EXEC mode (enter the password if prompted).
Example:
|
Step 2
|
show
sampler
sampler-name
The
show
sampler command shows the current status of the sampler that you specify.
Example:
Device# show sampler SAMPLER-1
Sampler SAMPLER-1:
ID: 2
Description: Sample at 50%
Type: random
Rate: 1 out of 2
Samples: 2482
Requests: 4964
Users (1):
flow monitor FLOW-MONITOR-1 (ip,Et0/0,I 2482 out of 4964
|
Configuration Examples for Flexible NetFlow Flow Sampling
Example: Configuring and Enabling a Random Sampler for IPv4 Traffic
The following example shows how to configure and enable random sampling for IPv4 output traffic.
This example starts in global configuration mode.
!
flow record v4_r1
match ipv4 tos
match ipv4 protocol
match ipv4 source address
match ipv4 destination address
match transport source-port
match transport destination-port
collect counter bytes long
collect counter packets long
!
flow monitor FLOW-MONITOR-1
record v4_r1
exit
!
sampler SAMPLER-1
mode random 1 out-of 2
exit
!
ip cef
!
interface GigabitEthernet 0/0/0
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 random sampling for IPv4 input traffic.
This example starts in global configuration mode.
!
flow record v4_r1
match ipv4 tos
match ipv4 protocol
match ipv4 source address
match ipv4 destination address
match transport source-port
match transport destination-port
collect counter bytes long
collect counter packets long
!
flow monitor FLOW-MONITOR-1
record v4_r1
exit
!
sampler SAMPLER-1
mode random 1 out-of 2
exit
!
ip cef
!
interface GigabitEthernet 0/0/0
ip address 172.16.6.2 255.255.255.0
ip 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:
Device(config)# interface GigabitEthernet 0/0/0
Device(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:
Device(config)# interface GigabitEthernet 0/0/0
Device(config-if)# no ip flow monitor FLOW-MONITOR-1 input
Device(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
ip flow monitor
command again without the sampler keyword and argument:
Device(config)# interface GigabitEthernet 0/0/0
Device(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.
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:
Device(config)# interface GigabitEthernet 0/0/0
Device(config-if)# no ip flow monitor FLOW-MONITOR-1 sampler SAMPLER-2 input
Device(config-if)# ip flow monitor FLOW-MONITOR-1 input
Additional References
Related Documents
Related Topic
|
Document Title
|
Cisco IOS commands
|
Cisco IOS Master Command List, All Releases
|
Flexible NetFlow conceptual information and configuration tasks
|
Flexible NetFlow Configuration Guide
|
Flexible NetFlow commands
|
Cisco IOS Flexible NetFlow Command Reference
|
Standards/RFCs
Standard
|
Title
|
No new or modified standards/RFCs are supported by this feature.
|
—
|
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
|
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 Flow Sampling
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.
Table 1 Feature Information for Flexible Netflow Flow Sampling
Feature Name
|
Releases
|
Feature Information
|
Flexible Netflow - Random Sampling
|
12.2(50)SY
12.4(20)T
Cisco IOS XE Release 3.1S
Cisco IOS XE Release 3.2SE
|
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
.
|