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If a computer receives an ARP Reply frame not intended for it, will it update its ARP Table?

Example: A, B and C are connected physically and locally. A broadcasts ARP Request to ask for B's MAC then B replies. Will computer C, upon receiving the frame, update its own ARP Table with B's IP and MAC? Or will the frame be dropped since it wasn't intended for C originally?

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2 Answers 2

up vote 3 down vote accepted

An ARP reply is unicast unlike the broadcasted request. So on a switched network computer C should never receive the packet if all is operating well. Even if it did get the reply it shouldn't register the packet unless it is promiscuous mode (even then I don't think it would add it to the ARP table, you might get different behavior on different OSes though).

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Depends on the configuration of at least C, because this is basically ARP spoofing. But the same mechanism is also used by some HA/failover software.

One way to find out is to try. ;-)

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