Switch ARP MAC – ARP and MAC Address Table

arpmacswitch

i know that this might be a little academic, but i was wondering.
let's assume we have an empty ARP table, and empty MAC Table.
let's assume PC A want to send a packet to PC B.

is the broadcast frame sent as a broadcast due to the ARP destenation or does it get flooded to all connected ports due to the empty MAC Address table. who'se "fault" is it ?

my guess is that it is because of the empty MAC TAble, the switch sent floods the frame, regardless to the ARP Dest. address

Best Answer

is the broadcast frame sent as a broadcast due to the ARP destenation

An ARP request's destination address is always the broadcast address.

or does it get flooded to all connected ports due to the empty MAC Address table.

The MAC address table in a switch is irrelevant for a broadcast frame. Broadcasts are always forwarded to all ports but the one they were received on.

You seem to be confusing broadcast forwarding with flooding. On a switch, the latter has the same result as the former, but flooding is due to the switch's inability to select the correct egress port when it hasn't learned a frame's unicast destination address (yet). Same result, different mechanisms. Think of flooding as a contingency measure (my mimicking a repeater hub) and broadcasting as a normal mechanism.

Flooded frames are generally ignored by connected host NICs, except for the one being addressed (or the ones being in promiscuous mode). This contrasts with broadcast frames which are received by all connected nodes.

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