1. When the switch receives a frame that is destined for an address that is not in the table (or for the broadcast address), the switch will flood the frame out of all ports other than the port on which it arrived.For example, frame 0, 00:ca:fe:58:75:bd > 00:16:3e:0f:43:74 is flooded on all ports except port 4, where it was received.
2. If the destination address is in the table, and is known to be reachable on the same port that the frame was received on, the switch will filter (drop) the frame.For example, frame 3, 3c:52:82:d4:0b:2c > 00:15:5d:b5:37:34 is not forwarded on any interface because it was received on port 2, and the destination address 00:15:5d:b5:37:34 was already in the forwarding table and known to be on port 2.
3. Otherwise, the switch will forward the frame out of the port corresponding to its destination address in the forwarding table.For example, frame 2, 00:ca:fe:58:75:bd > 3c:52:82:35:4d:98 is received on port 4, and its destination address 3c:52:82:35:4d:98 was already in the forwarding table and known to be on a different port, so that's where it was forwarded.

Suppose you observe the following ARP exchange on the top Ethernet segment:

00:50:56:11:0a:71 > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 56:
    Reply 192.168.55.181 is-at 00:50:56:11:0a:71, length 42

• Gratuitous ARP reply

An ARP reply that is sent without first receiving an ARP request is a gratuitous ARP reply. Note that the destination address in the Ethernet header is the broadcast address.

multicast mac address