Understanding NetFlow duplication: Why it happens, and how to deduplicate

NetFlow records can be duplicated when the same traffic conversation is exported by multiple interfaces or network devices, inflating volume measurements and distorting capacity planning and top-talker analysis. Ingress and egress duplication can be avoided by configuring monitoring only on egress interfaces, while multi-exporter duplication requires selecting authoritative devices or filtering records according to device roles and network topology. For internet-bound traffic, central border routers are often suitable reporting sources, whereas internal east-west traffic may require monitoring spine switches or load balancers, and cross-site traffic may need additional site-based filters to prevent counting flows at both tunnel endpoints. Datadog NetFlow Monitoring supports this approach by allowing users to tag network devices, such as with border, core, or site roles, and filter dashboards by those tags to obtain more accurate traffic views without necessarily disabling monitoring across the network.

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