1. Switches – Continued

2. Switches If a switch has N ports with multiple computers per port, then how many simultaneous transmissions can you have? Explain how you can have multiple computers attached to each port of the switch. Be able to draw a diagram if this situation If a switch has N ports, how many internal bridges must be present? See Figure 11.10 on p. 168

3. Switches Continued Switches (like Bridges) operate at Layer 2 (Data Link Layer) of the OSI model For management purposes, always save one switch port for administration. All traffic can be duplicated and sent to that port

4. Basic Logic of a LAN Switch A frame is received on a port If the destination is broadcast or multicast, forward to all ports If the destination is unicast and the address is not in the address table, forward to all ports If the destination is unicast and the address is in the address table, forward the frame to the associated port, unless the MAC address is associated with the incoming port. If so, discard the frame.

5. Switches Continued The switch creates separate Ethernet segments Each segment is called a collision domain because frames sent by devices on that segment can collide with other frames on that segment Important: Switches do not stop the flow of broadcasts (routers do)

6. Two Types of Switches Store-and Forward Cut-Through

7. Store-and-Forward Switch The switch fully receives all bits in the frame (store) before forwarding the frame (forward). This allows the switch to check the FCS (CRC bits) before forwarding the frame

8. Cut_Through Switch The switch performs the address table lookup as soon as the destination address field in the header is received The first bits in the frame can be sent out the outbound port before the final bits in the incoming frame are received This does not allow the switch to discard frames that fail the CRC check

9. Broadcast Domain A grouping of clients that all receive the same broadcasts Collision domains and broadcast domains are different