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 Flexible NetFlow 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. Supported Flexible NetFlow Fields The following tables provide a consolidated list of supported fields in Flexible NetFlow (FNF) for various traffic types and traffic direction. If the packet has a VLAN field, then that length is not accounted for. Note Configuring Flexible NetFlow Flow Samplers Field Layer 2 In Layer 2 Out IPv4 In IP v4 Out IPv6 In IPv6 Out Notes Key or Collect Fields Interface input Yes — Yes — Yes — If you apply a flow monitor in the input direction: • Use the match keyword and use the input interface as a key field.
• Use the collect keyword and use the output interface as a collect field. This field will be present in the exported records but with a value of 0. Configuring Flexible NetFlow 14