1. Layer 2 and Switching

2. How Computers Communicate  In a two node flat network data can be sent without addressing.

3. How Computers Communicate  What if there are more than two nodes on a network?  Like with mail you need to address the data.  In a flat network using a hub this is simple.

4. How Computers Communicate  Every computer receives all data that is sent and the computer must look at the address to decide what to do with it  To address the data MAC (Media Access Control) addresses are used.  A MAC address identifies the hardware (network card) of a computer on a local network

5. How Computers Communicate  A MAC address is a group of six two digit hexadecimal numbers  05:AF:2C:19:CF:2B  In most cases the first few sets of numbers represent the make (Dlink, 3Com) and the last numbers represent the specific device

6. How Hubs Work  All computers in the network are connected to the hub

7. How Hubs Work  Computer A sends the message “Hello” to Computer C

8. How Hubs Work  The hub sends the message to all computers connected to it

9. How Hubs Work  Computer B ignores the message and C replies

10. How Hubs Work  The hub sends the message to all computers connected to it

11. How Hubs Work  A receives the message and B ignores the message

12. Advantages and Disadvantages of Hubs  Pros Simple to build No logic needed  Cons Cannot handle large amounts of traffic Security More work for the client

13. Solution to Hubs  Switches solve the problems that hubs have.  Instead of sending the same data out on all ports the switch only sends the data to the port the computer is connected to.

14. How Switches Work  Switches keep track of which MAC is connected to which port.

15. How Switches Work  Computer A sends “Hello” to computer B

16. How Switches Work  The switch looks in the address table and finds B on port 2 and sends the data to the port.

17. How Switches Work  B receives the data and replies to A.

18. How Switches Work  The switch looks in the switching table and sends the data to A.

19. Advantages and Disadvantages of Switches  Pros More secure More efficient Clients only receive data addressed to them  Cons The switch need logic More expensive to build

20. Practice work  List some of the security concerns with using hubs.  List how these do not affect switches.  Bonus: How could sniff packets on a switched network? There’s not a lot of work that can be assigned at this point.