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 Outline  Overview  Functions of Ethernet Switches and Bridges  Frame Transmission Modes  How Switches and Bridges Learn Source MAC Addresses  How Switches and Bridges Forward and Filter Frames  Summary 43

44. cpe@rmutt Ethernet Switches and Bridges 44  Address learning  Forwarding the filtering decisions  Loop avoidance

45. cpe@rmutt Transmitting Modes 45

46. cpe@rmutt MAC Address Table 46 The initial MAC address table is empty.

47. cpe@rmutt Learning Addresses 47 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).

48. cpe@rmutt Learning Addresses (Cont.) 48 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).

49. cpe@rmutt Filtering Frames 49 Station A sends a frame to station C. The destination is known; the frame is not flooded.

50. cpe@rmutt Filtering Frames (Cont.) 50 Station A sends a frame to station B. The switch has the address for station B in the MAC address table.

51. cpe@rmutt Broadcast and Multicast Frames 51 Station D sends a broadcast or multicast frame. Broadcast and multicast frames are flooded to all ports other than the originating port.

52. cpe@rmutt 52 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

53. cpe@rmutt Transmitting Modes 53

54. cpe@rmutt Summary  Ethernet switches and bridges increase the available bandwidth of a network by creating dedicated network segments and interconnecting the segments.  Switches and bridges use one of three operating modes to transmit frames: store and forward, cut- through, and fragment-free.  Switches and bridges maintain a MAC address table to store address-to-port mappings so that they can determine the locations of connected devices.  When a frame arrives with a known destination address, the frame is forwarded only on the specific port connected to the destination station. 54

55. cpe@rmutt CONTINUE NEXT WEEK 55

56. cpe@rmutt 56 © 2004 Cisco Systems, Inc. All rights reserved. ICND v2.2—1-56 Identifying Problems That Occur in Redundant Switched Topologies

57. cpe@rmutt Outline  Overview  Redundant Switched and Bridged Topologies  Broadcast Storms  Multiple Frame Transmissions  MAC Database Instability  Summary 57

58. 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. 58

59. cpe@rmutt 59 Host X sends a broadcast. Switches continue to propagate broadcast traffic over and over. Broadcast Storms

60. cpe@rmutt 60 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

61. cpe@rmutt 61 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

62. cpe@rmutt Summary  Bridged and switched networks are commonly designed with redundant links and devices, which can introduce problems, such as broadcast storms, multiple frame transmission, and MAC database instability.  A broadcast storm is created when each switch on a redundant network floods broadcast frames endlessly.  Multiple frame transmissions occur when multiple copies of the same frame arrive at the intended host, potentially causing problems with the receiving protocol.  MAC database instability occurs when multiple copies of a frame arrive on different ports of a switch. 62

63. cpe@rmutt 63 © 2004 Cisco Systems, Inc. All rights reserved. ICND v2.2—1-63 Introducing Spanning Tree Protocol

64. cpe@rmutt Outline  Overview  Spanning Tree Protocol  Spanning Tree Operation  Root Bridge Selection  Spanning Tree Port States  Spanning Tree Path Costs  Spanning Tree Recalculation  Rapid Spanning Tree Protocol  Summary 64

65. cpe@rmutt Spanning Tree Protocol 65 Provides a loop-free redundant network topology by placing certain ports in the blocking state

66. cpe@rmutt 66 One root bridge per network One root port per nonroot bridge One designated port per segment Nondesignated ports are unused Spanning Tree Operation

67. cpe@rmutt 67 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

68. cpe@rmutt 68 Spanning Tree Port States (Cont.)

69. cpe@rmutt 69 Spanning Tree Operation

70. cpe@rmutt 70 Spanning Tree Path Cost

71. cpe@rmutt 71

72. cpe@rmutt 72

73. cpe@rmutt Spanning Tree Port States 73 Spanning tree transits each port through several different states:

74. cpe@rmutt Spanning Tree Recalculation 74

75. cpe@rmutt Spanning Tree Convergence 75 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.

76. cpe@rmutt Rapid Spanning-Tree Protocol 76

77. cpe@rmutt 77 Rapid Transition to Forwarding

78. cpe@rmutt Per VLAN Spanning Tree + 78

79. cpe@rmutt Summary  STP is a bridge-to-bridge protocol used to maintain a loop- free network.  To maintain a loop-free network topology, STP establishes a root bridge, a root port, and designated ports.  With STP, the root bridge has the lowest BID, which is made up of the bridge priority and the MAC address.  When STP is enabled, every bridge in the network goes through the blocking state and the transitory states of listening and learning at power up. If properly configured, the ports then stabilize to the forwarding or blocking state.  If the network topology changes, STP maintains connectivity by transitioning some blocked ports to the forwarding state.  RSTP significantly speeds the recalculation of the spanning tree when the network topology changes. 79

80. cpe@rmutt 80 © 2004 Cisco Systems, Inc. All rights reserved. ICND v2.2—2-80 Introducing VLAN Operations

81. cpe@rmutt Outline  Overview  VLANs Defined  VLAN Operation  VLAN Membership Modes  802.1Q Trunking  Inter-Switch Link Protocol and Encapsulation  VLAN Trunking Protocol Features  VTP Modes  VTP Operations  VTP Pruning  Summary 81

82. cpe@rmutt VLAN Overview 82 VLAN = Broadcast Domain = Logical Network (Subnet) Segmentation Flexibility Security

83. cpe@rmutt 83 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

84. cpe@rmutt VLAN Membership Modes 84

85. cpe@rmutt 802.1Q Trunking 85

86. cpe@rmutt Importance of Native VLANs 86

87. cpe@rmutt 802.1Q Frame 87

88. 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 88 ISL trunks enable VLANs across a backbone.

89. cpe@rmutt ISL Encapsulation 89

90. LOGO LAN Design Guide

91. cpe@rmutt LAN Segmentation 91 Segmentation allows network congestion to be significantly reduced within each segment.

92. cpe@rmutt Hierarchical Design Model: Access Layer 92

93. cpe@rmutt Access Layer 93

94. cpe@rmutt Functions of the Access Layer 94

95. cpe@rmutt Distribution Layer 95

96. cpe@rmutt Distribution Layer  In a switched network, the distribution layer includes several functions such as the following:  Aggregation of the wiring-closet connections  Broadcast/multicast domain definition  VLAN routing  Any media transitions that need to occur  Security 96

97. cpe@rmutt Core Layer 97 The core layer is a high-speed switching backbone. The core layer should be designed to switch packets as fast as possible.

98. cpe@rmutt Summary  A VLAN permits a group of users to share a common broadcast domain regardless of their physical location in the internetwork. VLANs improve performance and security in switched networks.  In a network, a Catalyst switch operates in a network like a traditional bridge. Each VLAN configured on the switch implements address learning, forwarding and filtering decisions, and loop avoidance mechanisms.  Ports belonging to a VLAN are configured with a membership mode that determines to which VLAN the ports belong. Catalyst switches support two VLAN membership modes: static and dynamic.  The IEEE 802.1Q protocol is used to transport frames for multiple VLANs between switches and routers and for defining VLAN topologies. 98

99. cpe@rmutt Summary (Cont.)  ISL is a Cisco proprietary protocol to transport multiple VLANs between switches and routers. ISL provides VLAN tagging capabilities while maintaining full wire-speed performance.  VTP is a Layer 2 messaging protocol that maintains VLAN configuration consistency by managing the additions, deletions, and name changes of VLANs across networks.  VTP operates in one of three modes: server, client, or transparent. The default VTP mode is server mode, but VLANs are not propagated over the network until a management domain name is specified or learned.  VTP advertisements are sent throughout the management domain every 5 minutes or when there is a change. The configuration revision number that is included in each advertisement identifies the most current information.  VTP pruning uses VLAN advertisements to determine when a trunk connection is flooding traffic needlessly. 99

100. cpe@rmutt Q & A 100