Why am I getting duplicate packet errors in my ARC log file?

Sometimes you will notice the following warning message in your ARC log file:

“||2012-01-10 00:22:10,972 WARN ElpWorkerThread-1 elp Duplicate packet from MAC xx:xx:xx:xx:xx:xx ,sequence 0x4132, expected sequence > 0x4132. Packet rejected.”

Packets being referred to in this message are duplicate packets and this is expected behavior from time to time. Tags communicate to the ARC with a feature called “Always ACK.” This causes ARC to send an acknowledgement to the tag for each packet it receives from the tag. If the tag does not receive an acknowledgement from the ARC in a timely fashion, it may retry its transmission utilizing the original sequence number. Sometimes during the sending of the second packet, the acknowledgement arrives for the first sent packet. This results in duplicate packets. When this happens ARC just discards the duplicate, handles the first packet, and notifies the user that a duplicate packet was received.

Duplicate packets are not known to cause any performance issues with the ARC and are not a cause for alarm.

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