why can I see a UDP Unicast from a third machine not involved in this conversation?

while doing regular packet troubleshooting I could see a UDP Unicast traffic from third machine NOT involved in this conversation, and I could not understand why ... could anyone explain?

Example

A <-------------------> B
                   |
                   C
Machine C could see some unicast traffic from A to B .
Happens from time to time in a VOIP traffic ... is this normal ?
LRBEDAsked:
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nociSoftware EngineerCommented:
Most likely:
If a switch has no knowlegde of where the packet really needs to go (The destination of that packet has not sent a packet recently)
then the switch will broadcast it. Any return traffic will setup the mac/cam table with the right interface for that MAC address.

Less likely: (because you only see one packet):
It might indicate that your switch lacks enough power to handle the traffic. [ to smal a mac/cam table, to match mac addresses to interfaces ]
If one interface overflows the machine on filtering & routing, then the swith will start broadcasting a packet.
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LRBEDAuthor Commented:
Thank you NOCI
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