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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
  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
                    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
    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
  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
        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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