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How to Configure Netflow on Cisco Nexus Switches


There are a few steps required to configure Netflow on Cisco Nexus switches.

Items that are between { } and in bold should be replaced with values specific to the environment being configured.

  1. Enable Netflow
config t
feature netflow
  1. Configure a Netflow Flow Record

A Netflow record details what information you want to collect. You can use the built in record, or create a custom record.

The built in record is:

N7K1# show flow record netflow-original
Flow record netflow-original:
   Description: Traditional IPv4 input NetFlow with origin AS
   No. of users: 1
   Template ID: 256
       match ipv4 source address
       match ipv4 destination address
       match ip protocol
       match ip tos
       match transport source-port
       match transport destination-port
        match interface input
        match interface output
        match flow direction
        collect routing source as
        collect routing destination as
        collect routing next-hop address ipv4
        collect transport tcp flags
        collect counter bytes
        collect counter packets
        collect timestamp sys-uptime first
        collect timestamp sys-uptime last
  1. Configure a Netflow Flow Exporter

Set destination to your Auvik collector’s IP address, and source to the interface name that will export flows to the collector.

N7K1(config)# flow exporter exporter-1
N7K1(config-flow-exporter)# description Fluke Collector
source Vlan10
transport udp 2055
version 9
  1. Configure a Netflow Flow Monitor

Flow Monitors bind the Flow Record to the Flow Exporter

N7K1(config)# flow monitor netflow-monitor-1
record custom-netflow-record
exporter exporter-1

or you can use the built-in Netflow Flow Record:

N7K1(config)# flow monitor netflow-monitor-2
record netflow-original
exporter exporter-2

You can also apply multiple exporters to the same monitor:

N7K1(config)# flow monitor netflow-monitor-3
record custom-netflow-record
exporter exporter-1
exporter exporter-2
  1. Apply the Netflow Monitor to the your L3 interfaces
interface eth3/10
ip flow monitor netflow-monitor-1 input
  1. (Optional) Configure a Netflow Sampler

Netflow samplers become important when you’re running mixed M1/F2(e) VDCs. Due to the L3 proxy routing required for F2(e), Netflow traffic is CPU processed. The CPU will automatically rate limit Netflow traffic to 1 out of a 1000 packets to protect the control plane. An error will prompt when trying to configure this in a mixed environment:

N7K1(config)# interface vlan 10
N7K1(config-if)#  ip flow monitor netflow-monitor-1 input
ERROR: A sampler must be configured for an interface on an F2 card or F2e mixed

Configure a sampler to sample 1 out of every 1000 packets:

N7K1(config)# sampler netflow-sampler
N7K1(config-flow-sampler)#  mode 1 out-of 1000
N7K1(config-flow-sampler)# exit
N7K1(config)# interface vlan 10
N7K1(config-if)#  ip flow monitor netflow-monitor-1 input sampler netflow-sampler

Recommended sampler is 1 out-of 4956 to avoid rate limiting.

An additional 1:100 sampler, over the configured sampler is applicable for F2/F2e ports

There will be a new message. The bottom part is important to understand. 

This says that whatever sampling rate you have configured, we will only sample 1 of those packets out of every 100. If the sampler was configured for 1 out of 1000, the actual sampling rate would be 1 out of 100,000. 

This could result in useless Netflow statistics. It is advised to set it to the maximum allowed by your environment.

sampler netflow-sampler
mode 1 out-of 10
  1. (Optional) Configure Netflow timers

These Netflow timers are available:

flow timeout active 120 (default is 1800 seconds)
flow timeout inactive 32 (default is 15 seconds)
flow timeout fast 32 threshold 100 (default is disabled)
flow timeout session (default is disabled)
flow timeout aggressive threshold 75 (default is disabled)

Show commands

show flow record netflow-original
show flow record custom-netflow-record
show flow exporter < This is where you'll see statistics
show flow monitor netflow-monitor
show sampler

Verify statistics:

N7K1# show flow export
Flow exporter exporter-1:
   Description: Fluke Collector
   VRF: default (1)
   Destination UDP Port 2055
   Source Interface Vlan10 (
   Export Version 9
   Exporter Statistics
       Number of Flow Records Exported 726
       Number of Templates Exported 1
       Number of Export Packets Sent 37
       Number of Export Bytes Sent 38712
       Number of Destination Unreachable Events 0
       Number of No Buffer Events 0
       Number of Packets Dropped (No Route to Host) 0
       Number of Packets Dropped (other) 0
       Number of Packets Dropped (LC to RP Error) 0
       Number of Packets Dropped (Output Drops) 0
       Time statistics were last cleared: Tue Jul  8 21:12:06 2014
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