ZyXEL GS1920 Series User Guide - Page 337

CHAPTER 42 MAC Table 42.1 MAC Table Overview This chapter introduces the MAC Table screen. The MAC Table screen (a MAC table is also known as a filtering database) shows how frames are forwarded or filtered across the Switch's ports. It shows what device MAC address, belonging to what VLAN group (if any) is forwarded to which port(s) and whether the MAC address is dynamic (learned by the Switch) or static (manually entered in the Static MAC Forwarding screen). 42.1.1 What You Can Do Use the MAC Table screen (Section 42.2 on page 338) to check whether the MAC address is dynamic or static. 42.1.2 What You Need to Know The Switch uses the MAC table to determine how to forward frames. See the following figure. 1 The Switch examines a received frame and learns the port on which this source MAC address came. 2 The Switch checks to see if the frame's destination MAC address matches a source MAC address already learned in the MAC table. • If the Switch has already learned the port for this MAC address, then it forwards the frame to that port. • If the Switch has not already learned the port for this MAC address, then the frame is flooded to all ports. Too much port flooding leads to network congestion. • If the Switch has already learned the port for this MAC address, but the destination port is the same as the port it came in on, then it filters the frame. GS1920 Series User's Guide 337