Figure 1 shows a four port switch with four PCs attached one to each port. The PCs are named A, B, C, and D. The abbreviated MAC addresses are 00-0A, 00-0B, 00-0C, and 00-0D. The switch MAC address table is also shown. A is sending a frame to D. The switch enters the source MAC address for A in the MAC address table. In Figure 2, the switch doesn’t have the MAC address for D in the MAC address table, so it forwards the frame from A out all other ports (2, 3, and 4).