The term packet duplication refers to reporting on the same traffic multiple times as it passes through interfaces on a switch. Several port mirroring configurations can result in duplication because traffic from all ports is forwarded to Multi-Port Monitor.
The presence of duplicate packets can skew the metrics that are collected. Packet loss statistics are affected because duplicate packets are viewed as retransmissions.
As a best practice, configure mirror ports to minimize or eliminate duplicate packets. Multi-Port Monitor provides a packet deduplication setting that applies to the capture card and is enabled by default. This setting discards packets that seem to be duplicates of packets that were already processed.
During initial port mirroring configuration, you can temporarily disable the global setting for packet deduplication. Disabling the setting lets you see duplicate packets, which can help you eliminate duplication from mirrored sessions.
Deduplication logic applies to all packets received on a given logical port. Therefore, a duplicate packet from the same VLAN is not discarded when it is received on a different logical port. If you combine two physical ports into one logical port definition, a duplicate is discarded in the following situations:
Both packets are retained if the two physical ports are not combined into a logical port.
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