Ethernet, defined under IEEE 802.3, is one of today’s most widely used data communications standards, and it finds its major use in LAN applications.

For Ethernet communications, the logical topology is a multi-access bus in which devices all use the same shared-media. However, the physical topology of most Ethernet networks today is that of a star or extended star. In the topology, end devices are typically connected, in a point-to-point basis, to a Layer 2 switch.

A Layer 2 switch performs switching and filtering based only on the MAC address. A Layer 2 switch builds a MAC address table that it uses to make forwarding decisions. Typical switch operations are:

• Learning: as each frame is received on each port, the switching software looks at the source address of the frame and adds that source address to the MAC table that the switch maintains.
• Flooding: the switch forwards the frame destined for an unknown station or with the broadcast destination address out all switch ports other than the one it was received on.
• Forwarding: the switch forwards the frame destined for a known station out specific port only.
• Filtering: the switch drops the frame destined for a station on the port that was received that frame.

More Understanding

• How Switches Learn MAC Addresses

References

• Layer 2 Switch Operation