The switch can learn the port mapping for the source host by reading and
learning the source MAC address in the frame, so the switch will add the source MAC
address, and the port it learned it on, to the port mapping table, or MAC address table.
Now the switch knows the source MAC address and what port to use when attempting
to reach that MAC address. For example, source MAC address is 0800:0222:2222 = out
port 1.
But, because the switch does not know which port the destination MAC is connected to yet,
and because it is doing an ARP broadcast, the destination address is a broadcast, so the
switch has to ?¬‚ood the packet, now called a Layer 2 frame, out all ports except for the
???source??? port. This is shown in Figure 2-8.
Figure 2-8 Switch Learning and Forwarding
DST MAC
Broadcast
SRC MAC
0800:0222:2222
ARP
Request
ARP
Request
Packet
Parking Lot
DST MAC
Broadcast
SRC MAC
0800:0222:2222
ARP
Request
Layer 3 = 192.168.3.2
Layer 2 = 0800:0222:1111
Layer 3 = 192.168.3.1
Layer 2 = 0800:0222:2222
Switch: Since the destination address is
broadcast, I??™ll flood the frame out all ports.
DST MAC
Broadcast
SRC MAC
0800:0222:2222
ARP
Request
Layer 3 = 192.168.3.2
Layer 2 = 0800:0222:1111
Layer 3 = 192.
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