1. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-1 Ethernet LANs Chapter 4 Updated January 2009 Raymond Panko’s Business Data Networks and Telecommunications, 7th edition May only be used by adopters of the book

2. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-2 4-1: A Short History of Ethernet Standards The 802 Committee –In the early 1980s, development passed to the Institute for Electrical and Electronics Engineers (IEEE) The IEEE created the 802 LAN/MAN Standards Committee for LAN standards –This committee is usually called the 802 Committee

3. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-3 4-1: A Short History of Ethernet Standards The 802 Committee –The 802 Committee creates working groups for specific types of standards 802.1 for general standards, including security standards 802.3 for Ethernet standards 802.11 for wireless LAN standards 802.16 for WiMax wireless metropolitan area network standards

4. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-4 4-1: A Short History of Ethernet Standards The 802.3 Working Group –This group is in charge of creating Ethernet standards –The terms 802.3 and Ethernet are interchangeable today –Ethernet standards govern physical layer processes –Ethernet also governs data link layer standards (frame organization, switch operation, etc.)

5. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-5 Ethernet Physical Layer Standards

6. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-6 4-2: Ethernet Physical Layer Standards UTP Physical Layer Standards Medium Required Maximum Run Length Speed 100BASE-TX4-pair Category 5 or higher100 meters100 Mbps 1000BASE-T (Gigabit Ethernet) 4-pair Category 5 or higher100 meters1,000 Mbps 10BASE-T4-pair Category 3 or higher100 meters10 Mbps 100BASE-TX dominates access links today, Although 1000BASE-T is growing in access links today

7. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-7 Fiber Physical Layer Standards Medium 850 nm light (inexpensive) Multimode fiber Maximum Run Length Speed 1000BASE-SX275 m1 Gbps 1000BASE-SX500 m1 Gbps 1000BASE-SX220 m1 Gbps 1000BASE-SX550 m1 Gbps 4-2: Ethernet Physical Layer Standards 62.5 microns 160 MHz-km 62.5200 50400 50500 The 1000BASE-SX optical fiber standard dominates trunk links today S means that the standard uses short wavelength light (850 nm)

8. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-8 4-3: Baseband Versus Broadband Transmission The “BASE” in Ethernet standards refers to baseband transmission. In baseband transmission, the signal is merely injected into the wire or fiber cord and then propagates down the wire. This is inexpensive, so baseband transmission dominates Ethernet transmission today.

9. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-9 4-3: Baseband Versus Broadband Transmission In broadband transmission, the signal is modulated to propagate in a radio channel.

10. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-10 4-5: Data Link Using Multiple Switches Original Signal Received Signal Regenerated Signal Switches regenerate signals before sending them out; this removes propagation effects It therefore allows signals to travel farther

11. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-11 Figure 4-5: Data Link Using Multiple Switches Original Signal Received Signal Received Signal Received Signal Regenerated Signal Regenerated Signal Thanks to regeneration, signals can travel far across a series of switches

12. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-12 Ethernet Data Link Layer Standards The MAC Layer: Frame Organization Switch Operation

13. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-13 Figure 4-6: Layering in 802 Networks TCP/IP Internet Layer Standards (IP, ARP, etc.) Other Internet Layer Standards (IPX, etc.) 802.2 Ethernet 802.3 MAC Layer Standard Physical Layer Media Access Control Layer Non-Ethernet MAC Standards (802.5, 802.11, etc.) 100BASE- TX 1000 BASE- SX … Logical Link Control Layer Non-Ethernet Physical Layer Standards (802.11, etc.) Data Link Layer Internet Layer Ethernet has many physical layer standards (Fig. 4-2) But Ethernet only has a single MAC standard (The 802.3 MAC Layer Standard)

14. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-14 Figure 4-6: Layering in 802 Networks TCP/IP Internet Layer Standards (IP, ARP, etc.) Other Internet Layer Standards (IPX, etc.) 802.2 Ethernet 802.3 MAC Layer Standard Physical Layer Media Access Control Layer Non-Ethernet MAC Standards (802.5, 802.11, etc.) 100BASE- TX 1000 Base- SX … Logical Link Control Layer Non-Ethernet Physical Layer Standards (802.11, etc.) Data Link Layer Internet Layer The 802 LAN/MAN Standards Committee subdivided the data link layer The media access control (MAC) layer handles details specific to a particular technology (Ethernet 802.3, 802.11 for wireless LANs, etc.) The logical link control layer handles some general functions: Connection to the internet layer, etc.; Not important to corporate networking professionals

15. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-15 4-7: The Ethernet MAC-Layer Frame

16. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-16 4-7: The Ethernet MAC-Layer Frame Header –Preamble Field A series of 7 octets Each octet is 10101010 Provides a synchronizing signal for the receiver’s clock Like a quarterback saying, “Hut one, hut two, hike!” –Start of Frame Delimiter Field A single octet of 10101011 (does not end in 10) Finishes the synchronization Preamble (7 octets) Start of Frame Delimiter (1 octet)

17. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-17 4-7: The Ethernet MAC-Layer Frame Header –Destination and source MAC addresses –Each is 48 bits long –Computers and switches work with the 48-bit numbers –For humans, converted into hexadecimal notation Base 16 –Look like: A1-1B-23-DF-FF-00 Six pairs of symbols separated by dashes Each symbol represents four bits Symbols are 0 through 9 or A through F Start of Frame Delimiter (1 octet) Destination MAC Address (48 bits) Source MAC Address (48 bits)

18. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-18 Figure 4-8: Hexadecimal Notation 4 Bits*Decimal (Base 10) Hexadecimal (Base 16) 4 Bits*Decimal (Base 10) Hexadecimal (Base 16) 000000 hex100088 hex 000111 hex100199 hex 001022 hex101010A hex 001133 hex101111B hex 010044 hex110012C hex 010155 hex110113D hex 011066 hex111014E hex 011177 hex111115F hex *Note: With 4 bits, there can be 2 4 = 16 possible “Hex” symbols…

19. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-19 Figure 4-8: Hexadecimal Notation To convert a 48-bit MAC address to “hex” –Short for hexadecimal (Base 16) counting –Divide a MAC address into 6 octets –Divide each octet into two 4-bit “nibbles” So 10000001 becomes 1000 0001 –Change each nibble to a hex symbol –1000 = A and 0001 is 1 –Write the two hex symbols together as A1 –Separate the six octets of the MAC address with dashes A1-2B-39-FD-FF-FF

20. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-20 4-7: Ethernet MAC Layer Frame Length –Length field gives the length of the data field in octets Data Field –LLC subheader (7 octets) that describes the contents of the rest of the data field –Followed (usually) by an IP packet PAD –Added by sender if the data field is less than 46 octets –If added, PAD is long enough to bring the data field plus the PAD to 46 octets

21. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-21 4-7: Ethernet MAC Layer Frame Question 1 –If the length field has the value 150, how long is the IP packet it carries? Question 2 –If the length field value is 400, how long is the PAD? Question 3 –If the length field value is 15, –How long is the IP packet in the data field? –How long is the PAD?

22. © 2009 Pearson Education, Inc. Publishing as Prentice Hall Field Preamble (7 octets of 10101010 for synchronization Start Frame Delimiter (10101011 to end synch) Destination MAC address (48 bits) Source MAC address (48 bits) Length (2 octets) Logical Link Control (LLC subheader, 8 octets) Packet (variable length) PAD (Situation-Specific) Frame Check Sequence 22 4.7: Ethernet MAC Layer Frame The Frame Check Sequence field is for error detection. If an error is found, the frame is discarded. There is no error message or request for transmission. Ethernet is not reliable. The Frame Check Sequence field is for error detection. If an error is found, the frame is discarded. There is no error message or request for transmission. Ethernet is not reliable.

23. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-23 Multi-Switch Ethernet LAN Operation

24. © 2009 Pearson Education, Inc. Publishing as Prentice Hall © 2011 Pearson Education, Inc. Publishing as Prentice Hall 24 Multiswitch Ethernet LAN A packet from A1… to E5…. Must pass through Switches 1, 2, and 3.

25. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-25 4-9: Multiswitch Ethernet LAN Switch 2 Switch 1 Switch 3 Port 5 on Switch 1 to Port 3 on Switch 2 Port 7 on Switch 2 to Port 4 on Switch 3 A1-44-D5-1F-AA-4C Switch 1, Port 2 E5-BB-47-21-D3-56 Switch 3, Port 6 D5-47-55-C4-B6-9F Switch 3, Port 2 B2-CD-13-5B-E4-65 Switch 1, Port 7 The Situation: A1… Sends to E5… Frame must go through 3 switches along the way (1, 2, and then 3)

26. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-26 4-9: Multiswitch Ethernet LAN Switching Table Switch 1 PortStation 2A1-45-D5-1F-AA-4C 7B2-CD-13-5B-E4-65 5D5-47-55-C4-B6-9F 5E5-BB-47-21-D3-56 Switch 2 Switch 1 Port 5 on Switch 1 to Port 3 on Switch 2 A1-44-D5-1F-AA-4C Switch 1, Port 2 B2-CD-13-5B-E4-65 Switch 1, Port 7 E5-BB-47-21-D3-56 Switch 3, Port 6 Host A1…creates a frame addressed to E5… Host A1… sends the frame to Switch 1. The switch accepts the frame coming in Port 2

27. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-27 4-9: Multiswitch Ethernet LAN Switching Table Switch 1 PortStation 2A1-45-D5-1F-AA-4C 7B2-CD-13-5B-E4-65 5D5-47-55-C4-B6-9F 5E5-BB-47-21-D3-56 Switch 2 Switch 1 Port 5 on Switch 1 to Port 3 on Switch 2 A1-44-D5-1F-AA-4C Switch 1, Port 2 B2-CD-13-5B-E4-65 Switch 1, Port 7 E5-BB-47-21-D3-56 Switch 3, Port 6 On Switch 1 Switch 1 looks up the destination MAC address and notes the port number for that address (Port 5) Switch 1 sends the frame out Port 5 Switch 2 is out that port

28. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-28 4-9: Multiswitch Ethernet LAN Switch 2 Switch 1 Switch 3 Port 5 on Switch 1 to Port 3 on Switch 2 Port 7 on Switch 2 to Port 4 on Switch 3 Switching Table Switch 2 PortStation 3A1-44-D5-1F-AA-4C 3B2-CD-13-5B-E4-65 7D5-47-55-C4-B6-9F 7E5-BB-47-21-D3-56 On Switch 2 Switch 2 repeats the process Notes that E5 … uses Port 7 Switch 2 sends the frame out Port 7 The frame goes to Switch 3

29. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-29 4-9: Multiswitch Ethernet LAN Switch 2 Switch 3 Port 7 on Switch 2 to Port 4 on Switch 3 A1-44-D5-1F-AA-4C Switch 1, Port 2 D5-47-55-C4-B6-9F Switch 3, Port 2 Switching Table Switch 3 PortStation 4A1-44-D5-1F-AA-4C 4B2-CD-13-5B-E4-65 2D5-47-55-C4-B6-9F 6E5-BB-47-21-D3-56 E5-BB-47-21-D3-56 Switch 3, Port 6 On Switch 3 Switch 3 repeats the process Sends the frame out Port 6 This takes the frame to the destination host

30. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-30 4-10: Hierarchical Ethernet LAN Ethernet switches must be arranged in a hierarchical topology In a hierarchical LAN, there is only one possible path between any hosts

31. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-31 4-11: Single Point of Failure and 802.1D In a hierarchy, If a switch or trunk line fails, there is no backup These backup links are disabled until a breakdown occurs. Then 802.1w Enables them. the 802.1w Rapid Spanning Tree Protocol allows backup links 2

32. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-32 Hub Versus Switch Operation Box

33. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-33 4-15: Hub Versus Switch Operation Today, Switches Dominate in Ethernet –A frame comes in one port –The switch looks up the frame’s destination MAC address in the switching table –The switch sends the frame out a single port –Only two ports are tied up –Other conversations can take place on other port pairs simultaneously Figure 4-16 Box

34. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-34 4-15: Hub versus Switch Operation Today, Switches Dominate in Ethernet –Earlier Ethernet networks used hubs –When a bit came in one port, the hub broadcast the bit out through all other ports –If A is transmitting, B and all other stations have to wait until A finishes transmitting –Otherwise, their signals will collide, and both will be unreadable –Media access control (MAC) prevents this Figure 4-16 Box

35. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-35 4-15: Hub versus Switch Operation CSMA/CD –The Ethernet hub MAC protocol –CSMA (carrier sense multiple access) If a station wants to transmit If no station is already transmitting, it may send immediately If another station is already sending, it must wait a random amount of time –After that random amount of time, the station begins CSMA again –Does NOT simply send after a wait if another station is transmitting Box

36. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-36 4-15: Hub versus Switch Operation CSMA/CD –CD (collision detection) If there is a collision because two stations send at the same time, all stations stop transmitting, wait a random period of time, and It must then apply CSMA again (it may not transmit simply because the random period of time is over) Box

37. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-37 4-15: Hub versus Switch Operation Latency –When one station transmits, others must wait –This creates latency –Latency became bad in large Ethernet hub networks –Switches solved this problem by avoiding the need to wait –Multiple conversations can take place simultaneously Box

38. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-38 Ethernet Security

39. © 2009 Pearson Education, Inc. Publishing as Prentice Hall The Threat: –Someone can enter a business and plug a computer into a wall jack. –This will give access to the network without going through the firewall. The Countermeasure: –Require anyone plugging into an Ethernet switch to authenticate himself or herself before being allowed beyond the switch. 39 6.17: Ethernet 802.1X Security

40. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-40 4-21: 802.1X Ethernet Port-Based Access Control Danger: An attacker will walk in and plug into a wall jack This bypasses the border firewall Solution: Authenticate everyone who connects to an access switch 802.1X standardizes this authentication

41. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-41 4-21: 802.1X Ethernet Port-Based Access Control Client PC is called the supplicant It sends credentials (proof of identity) to the switch The switch is called the network access server The NAS sends the credentials onto a central authentication server Credentials

42. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-42 4-21: 802.1X Ethernet Port-Based Access Control Authentication server usually is a RADIUS server Authentication server checks credentials against its authentication database Credentials

43. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-43 4-21: 802.1X Ethernet Port-Based Access Control Credentials Centralizing credential checking brings consistency No matter what switch the computer plugs into, It will be authenticated with the same credentials database Also, this database can be updated instantly if needed

44. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-44 4-21: 802.1X Ethernet Port-Based Access Control RADIUS server sends accept or reject message to NAS Switch accepts or rejects the supplicant client Accept/ Reject Accept/ Reject

45. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-45 Routed LANs Not all LANs are switched networks Some are routed networks (especially large LANs)

46. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-46 4-23: Routed LAN with Ethernet Subnets When a routed LAN links multiple Ethernet switched networks, individual switched networks are called subnets