1. LOGO Local Area Network (LAN) Layer 2 Switching and Virtual LANs (VLANs) Local Area Network (LAN) Layer 2 Switching and Virtual LANs (VLANs) Chapter 6

2. cpe@rmutt Objectives 2

3. cpe@rmutt Bridges 3

4. cpe@rmutt 802.3 LAN Development: Today’s LANs 4

5. cpe@rmutt Devices Function at Layers 5

6. cpe@rmutt Factors that Impact Network Performance  Network traffic (congestion).  Multitasking desktop operating systems (Windows, UNIX, and Mac) allow simultaneous network transactions.  Faster desktop operating systems (Windows, UNIX, and Mac) can initiate faster network activity.  Increased number of client/server applications using shared network data. 6

7. cpe@rmutt Network Congestion 7

8. cpe@rmutt Half-Duplex Ethernet Design 8

9. cpe@rmutt LAN Segmentation 9 Segmentation allows network congestion to be significantly reduced within each segment.

10. cpe@rmutt LAN Segmentation with Bridges 10

11. cpe@rmutt LAN Segmentation with Routers 11

12. cpe@rmutt LAN Segmentation with Switches 12

13. cpe@rmutt Ethernet Technologies 13

14. cpe@rmutt Types of Ethernet 14

15. cpe@rmutt Parameters for 10 Mbps Ethernet Operation 15

16. cpe@rmutt Ethernet Frame 16

17. cpe@rmutt Manchester Encoding Examples 17

18. cpe@rmutt 10BASE5 Architecture Example 18

19. cpe@rmutt 10BASE2 Network Design Limits 19

20. cpe@rmutt 10BASE-T Modular Jack Pinouts 20

21. cpe@rmutt 10BASE-T Repeated Network Design Limits 21

22. cpe@rmutt Parameters for 100-Mbps Ethernet Operation 22

23. cpe@rmutt Ethernet Frame 23

24. cpe@rmutt MLT-3 Encoding Example 24

25. cpe@rmutt 100BASE-TX Modular Jack Pinout 25

26. cpe@rmutt NRZI Encoding Examples 26

27. cpe@rmutt 100BASE-FX Pinout 27

28. cpe@rmutt Example of Architecture Configuration and Cable Distances 28

29. cpe@rmutt Types of Ethernet 29

30. cpe@rmutt Parameters for Gigabit Ethernet Operation 30

31. cpe@rmutt Ethernet Frame 31

32. cpe@rmutt Outbound (Tx) 1000Base-T Signal 32

33. cpe@rmutt Actual 1000Base-T Signal Transmission 33

34. cpe@rmutt Benefits of Gigabit Ethernet on Fiber 34

35. cpe@rmutt Gigabit Ethernet Layers 35

36. cpe@rmutt 1000BASE-SX and LX 36

37. cpe@rmutt Gigabit Ethernet Media Comparison 37

38. cpe@rmutt Gigabit Ethernet Architecture 38 Maximum 1000BASE-SX Cable Distances Maximum 1000BASE-LX Cable Distances

39. cpe@rmutt Parameters for 10-Gbps Ethernet Operation 39

40. cpe@rmutt 10GBASE LX-4 Signal Multiplexing 40

41. cpe@rmutt 10-Gigabit Ethernet Implementations 41

42. cpe@rmutt 42 © 2004 Cisco Systems, Inc. All rights reserved. ICND v2.2—1-42 Introducing Basic Layer 2 Switching and Bridging Functions

43. cpe@rmutt Ethernet Switches and Bridges 43  Address learning  Forwarding the filtering decisions  Loop avoidance

44. cpe@rmutt Transmitting Modes 44

45. cpe@rmutt MAC Address Table 45 The initial MAC address table is empty.

46. cpe@rmutt Learning Addresses 46 Station A sends a frame to station C. The switch caches the MAC address of station A to port E0 by learning the source address of data frames. The frame from station A to station C is flooded out to all ports except port E0 (unknown unicasts are flooded).

47. cpe@rmutt Learning Addresses (Cont.) 47 Station D sends a frame to station C. The switch caches the MAC address of station D to port E3 by learning the source address of data frames. The frame from station D to station C is flooded out to all ports except port E3 (unknown unicasts are flooded).

48. cpe@rmutt Filtering Frames 48 Station A sends a frame to station C. The destination is known; the frame is not flooded.

49. cpe@rmutt Filtering Frames (Cont.) 49 Station A sends a frame to station B. The switch has the address for station B in the MAC address table.

50. cpe@rmutt Broadcast and Multicast Frames 50 Station D sends a broadcast or multicast frame. Broadcast and multicast frames are flooded to all ports other than the originating port.

51. cpe@rmutt 51 Cut-Through Switch checks destination address and immediately begins forwarding frame Fragment-Free Switch checks the first 64 bytes, then immediately begins forwarding frame Store and Forward Complete frame is received and checked before forwarding Transmitting Frames

52. cpe@rmutt Transmitting Modes 52

53. cpe@rmutt CONTINUE NEXT WEEK 53

54. cpe@rmutt 54 © 2004 Cisco Systems, Inc. All rights reserved. ICND v2.2—1-54 Identifying Problems That Occur in Redundant Switched Topologies

55. cpe@rmutt Redundant Topology  Redundant topology eliminates single points of failure.  Redundant topology causes broadcast storms, multiple frame copies, and MAC address table instability problems. 55

56. cpe@rmutt 56 Host X sends a broadcast. Switches continue to propagate broadcast traffic over and over. Broadcast Storms

57. cpe@rmutt 57 Host X sends a unicast frame to router Y. The MAC address of router Y has not been learned by either switch. Router Y will receive two copies of the same frame. Multiple Frame Copies

58. cpe@rmutt 58 Host X sends a unicast frame to router Y. The MAC address of router Y has not been learned by either switch. Switches A and B learn the MAC address of host X on port 0. The frame to router Y is flooded. Switches A and B incorrectly learn the MAC address of host X on port 1. MAC Database Instability

59. cpe@rmutt 59 © 2004 Cisco Systems, Inc. All rights reserved. ICND v2.2—1-59 Introducing Spanning Tree Protocol

60. cpe@rmutt Spanning Tree Protocol 60 Provides a loop-free redundant network topology by placing certain ports in the blocking state

61. cpe@rmutt 61 One root bridge per network One root port per nonroot bridge One designated port per segment Nondesignated ports are unused Spanning Tree Operation

62. cpe@rmutt 62 BPDU = Bridge Protocol Data Unit (default = sent every two seconds) Root bridge = bridge with the lowest bridge ID Bridge ID = In this example, which switch has the lowest bridge ID? Spanning Tree Protocol Root Bridge Selection

63. cpe@rmutt 63 Spanning Tree Port States (Cont.)

64. cpe@rmutt 64 Spanning Tree Operation

65. cpe@rmutt 65 Spanning Tree Path Cost

66. cpe@rmutt 66

67. cpe@rmutt 67

68. cpe@rmutt 68

69. cpe@rmutt The Active Topology After Spanning Tree Is Complete 69

70. cpe@rmutt Spanning Tree Port States 70 Spanning tree transits each port through several different states:

71. cpe@rmutt Spanning Tree Recalculation 71

72. cpe@rmutt Spanning Tree Convergence 72 Convergence occurs when all the switch and bridge ports have transitioned to either the forwarding or the blocking state. When the network topology changes, switches and bridges must recompute STP, which disrupts user traffic.

73. cpe@rmutt Rapid Spanning-Tree Protocol 73

74. cpe@rmutt 74 Rapid Transition to Forwarding

75. cpe@rmutt Per VLAN Spanning Tree + 75

76. cpe@rmutt 76 © 2004 Cisco Systems, Inc. All rights reserved. ICND v2.2—2-76 Introducing VLAN Operations

77. cpe@rmutt VLAN Overview 77 VLAN = Broadcast Domain = Logical Network (Subnet) Segmentation Flexibility Security

78. cpe@rmutt 78 Each logical VLAN is like a separate physical bridge. VLANs can span across multiple switches. Trunks carry traffic for multiple VLANs. Trunks use special encapsulation to distinguish between different VLANs. VLAN Operation

79. cpe@rmutt VLAN Membership Modes 79

80. cpe@rmutt 802.1Q Trunking 80

81. cpe@rmutt Importance of Native VLANs 81

82. cpe@rmutt 802.1Q Frame 82

83. cpe@rmutt ISL Tagging  Performed with ASIC  Not intrusive to client stations; ISL header not seen by client  Effective between switches, and between routers and switches 83 ISL trunks enable VLANs across a backbone.

84. cpe@rmutt ISL Encapsulation 84

85. cpe@rmutt Q & A Q&A 85