Layer 3 switch:

Q: What is the difference between a layer 3 switch and a router?

A: In the switch the routing is implemented using hardware (Application Specific Integrated Circuit) instead of software and a microprocessor..

Q: Layer 3 switches can help  to reduce broadcast domains. Why?

A: Layer 3 switches do not forward any broadcasts to or from other connected networks, because this is a layer 2 function. The multicast function offers the possibility to send broadcasts to one or more chosen domains.

Q: Similar to the layer 2 switch, the destinations (here: subnets) are assigned to a physical interface. Where is this information stored?

A: The information is stored in "routing tables" with information about destination subnets, interfaces and additional routing protocol related information (e.g. hops, desirabilty).

Routing:

Q: What method is used to determine the correspondent destination subnet to an IP Address?

A: After an AND operation with the IP address and each subnet mask entry of the routing table, the "longest match lookup" determines which interface is used.

Layer 4 switch:

Q: The layer 4 switch offers "Quality of Service". On which information is the prioritisation based?

A: The quality of service is based on layer 4 Information: the port (e.g. HTTP, SMTP, POP3, telnet)