Understanding Flow Aggregation
You can collect an aggregate of sampled flows and send the aggregate to a specified host that runs either the cflowd application available from CAIDA (http://www.caida.org) or the newer version 9 format defined in RFC 3954, Cisco Systems NetFlow Services Export Version 9. Before you can perform flow aggregation, the routing protocol process must export the autonomous system (AS) path and routing information to the sampling process.
By using flow aggregation, you can obtain various types of byte and packet counts of flows through a router. The application collects the sampled flows over a period of 1 minute. At the end of the minute, the number of samples to be exported are divided over the period of another minute and are exported over the course of the same minute.
You configure flow aggregation in different ways, depending on whether you want to export flow records in cflowd version 5 or 8 format, or the separate version 9 format. The latter allows you to sample MPLS, IPv4, IPv6, and peer AS billing traffic. You can also combine configuration statements between the MPLS and IPv4 formats.
When PIC-based sampling is enabled, collection of flow statistics for sampled packets on flows in virtual private networks (VPNs) is also supported. No additional CLI configuration is required.