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Unknown Unicast

what is unknown unicast ?
I know that a switch learns the SMAC and adds it to the CAM table, let's say that a switch receives a frame with DMAC not in  its CAM table, by default it floods such frames.
So if i block unknown unicast, what will the switch do ?
 
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If you block unknown unicast packets the switch will drop any packets that have an unknown dmac.
This provides an extra bit of security against flooding attacks. While flooding may be helpful in some cases, the risks usually out weight the benefits. There should be enough packet flow during normal operations to keep the cam table up to date.
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tpat

ASKER

let's say that we have two hosts Host A, Host B connected to a switch.
what if the host A wants to communicate with host B, and host A sends a unknown unicast to host B as there is no CAM table entry for host B on the switch, so if i configure, not to flood unknown unicast on the switch how will host A be able to communicate with host B.
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