Configuring Timers

To configure time periods for active flow monitoring and intervals of inactivity, include the flow-active-timeout and flow-inactive-timeout statements at the [edit forwarding-options monitoring name output] hierarchy level:

• The flow-active-timeout statement specifies the time interval between flow exports for active flows. If the interval between the time the last packet was received and the time the flow was last exported exceeds the configured value, the flow is exported.

  This timer is needed to provide periodic updates when a flow has a long duration. The active timeout setting enables the router to retain the start time for the flow as a constant and send out periodic cflowd reports. This in turn allows the collector to register the start time and determine that a flow has survived for a duration longer than the configured active timeout.

  Note: In active flow monitoring, the cflowd records are exported after a time period that is a multiple of 60 seconds and greater than or equal to the configured active timeout value. For example, if the active timeout value is 90 seconds, the cflowd records are exported at 120-second intervals. If the active timeout value is 150 seconds, the cflowd records are exported at 180-second intervals, and so forth.

• The flow-inactive-timeout statement specifies the interval of inactivity for a flow that triggers the flow export. If the interval between the current time and the time that the last packet for this flow was received exceeds the configured inactive timeout value, the flow is allowed to expire.

  If the flow stops transmitting for longer than the configured inactive timeout value, the router purges it from the flow table and exports the cflowd record. As a result, the flow is forgotten as far as the PIC is concerned and if the same 5-tuple appears again, it is assigned a new start time and considered a new flow.

Both timers are necessary. The active timeout setting is needed to provide information for flows that constantly transmit packets for a long duration. The inactive timeout setting enables the router to purge flows that have become inactive and would waste tracking resources.

Note: The router must contain an Adaptive Services, MultiServices, or Monitoring Services PIC for the flow-active-timeout and flow-inactive-timeout statements to take effect.