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

2. 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
               Fields:
                   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

3. 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
                               destination 10.255.255.100
                               source Vlan10
                               transport udp 2055
                               version 9

4. 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

5. Apply the Netflow Monitor to the your L3 interfaces

   interface eth3/10   
      ip flow monitor netflow-monitor-1 input    
      exit

6. (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 vdc

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

   N7K1(config)# sampler netflow-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.
   Note: It is advised to set it to the maximum allowed by your environment.

             sampler netflow-sampler
                     mode 1 out-of 10

7. (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 
   show flow monitor netflow-monitor
   show sampler

   Verify statistics:

   N7K1# show flow export
   Flow exporter exporter-1:
       Description: Fluke Collector
       Destination: 10.255.255.100
       VRF: default (1)
       Destination UDP Port 2055
       Source Interface Vlan10 (10.10.10.5)
       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