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.
- Enable Netflow
config t
feature netflow
- 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
- 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
- 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
- Apply the Netflow Monitor to the your L3 interfaces
interface eth3/10
ip flow monitor netflow-monitor-1 input
exit
- (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
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
- (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
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