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.

LOGO

Local Area Network (LAN)

Layer 2 Switching and Virtual LANs (VLANs)

Local Area Network (LAN)

Layer 2 Switching and Virtual LANs (VLANs)

Chapter 6Chapter 6

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Objectives

2

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Bridges

3

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802.3 LAN Development: Today’s LANs

4

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Devices Function at Layers

5

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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

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Network Congestion

7

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Half-Duplex Ethernet Design

8

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LAN Segmentation

9

Segmentation allows network congestion to be significantly reduced within each segment.

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LAN Segmentation with Bridges

10

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LAN Segmentation with Routers

11

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LAN Segmentation with Switches

12

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Ethernet Technologies

13

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Types of Ethernet

14

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Parameters for 10 Mbps Ethernet Operation

15

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Ethernet Frame

16

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Manchester Encoding Examples

17

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10BASE5 Architecture Example

18

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10BASE2 Network Design Limits

19

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10BASE-T Modular Jack Pinouts

20

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10BASE-T Repeated Network Design Limits

21

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Parameters for 100-Mbps Ethernet Operation

22

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Ethernet Frame

23

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MLT-3 Encoding Example

24

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100BASE-TX Modular Jack Pinout

25

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NRZI Encoding Examples

26

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100BASE-FX Pinout

27

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Example of Architecture Configuration and Cable Distances

28

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Types of Ethernet

29

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Parameters for Gigabit Ethernet Operation

30

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Ethernet Frame

31

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Outbound (Tx) 1000Base-T Signal

32

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Actual 1000Base-T Signal Transmission

33

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Benefits of Gigabit Ethernet on Fiber

34

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Gigabit Ethernet Layers

35

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1000BASE-SX and LX

36

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Gigabit Ethernet Media Comparison

37

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Gigabit Ethernet Architecture

38

Maximum 1000BASE-SX Cable Distances

Maximum 1000BASE-LX Cable Distances

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Parameters for 10-Gbps Ethernet Operation

39

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10GBASE LX-4 Signal Multiplexing

40

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10-Gigabit Ethernet Implementations

41

cpe@rmutt42© 2004 Cisco Systems, Inc. All rights reserved. ICND v2.2—1-42

Introducing Basic Layer 2 Switching and

Bridging Functions

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Ethernet Switches and Bridges

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Address learning Forwarding the filtering decisions Loop avoidance

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Transmitting Modes

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MAC Address Table

45

• The initial MAC address table is empty.

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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).

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Learning Addresses (Cont.)

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• 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).

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Filtering Frames

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• Station A sends a frame to station C.

• The destination is known; the frame is not flooded.

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Filtering Frames (Cont.)

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• Station A sends a frame to station B.

• The switch has the address for station B in the MAC address table.

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Broadcast and Multicast Frames

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• Station D sends a broadcast or multicast frame.

• Broadcast and multicast frames are flooded to all ports other than the originating port.

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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

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Transmitting Modes

52

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CONTINUE NEXT WEEK

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cpe@rmutt54© 2004 Cisco Systems, Inc. All rights reserved. ICND v2.2—1-54

Identifying Problems That Occur in Redundant

Switched Topologies

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Redundant Topology

Redundant topology eliminates single points of failure. Redundant topology causes broadcast storms, multiple frame

copies, and MAC address table instability problems.55

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• Host X sends a broadcast. • Switches continue to propagate broadcast traffic

over and over.

Broadcast Storms

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• 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

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• 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

cpe@rmutt59© 2004 Cisco Systems, Inc. All rights reserved. ICND v2.2—1-59

Introducing Spanning Tree Protocol

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Spanning Tree Protocol

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• Provides a loop-free redundant network topology by placing certain ports in the blocking state

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• One root bridge per network• One root port per nonroot bridge• One designated port per segment• Nondesignated ports are unused

Spanning Tree Operation

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• 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

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Spanning Tree Port States (Cont.)

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Spanning Tree Operation

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Spanning Tree Path Cost

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The Active Topology After Spanning Tree Is Complete

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Spanning Tree Port States

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• Spanning tree transits each port through several different states:

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Spanning Tree Recalculation

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Spanning Tree Convergence

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• 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.

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Rapid Spanning-Tree Protocol

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Rapid Transition to Forwarding

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Per VLAN Spanning Tree +

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cpe@rmutt76© 2004 Cisco Systems, Inc. All rights reserved. ICND v2.2—2-76

Introducing VLAN Operations

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VLAN Overview

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VLAN = Broadcast Domain = Logical Network (Subnet)

• Segmentation

• Flexibility

• Security

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• 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

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VLAN Membership Modes

79

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802.1Q Trunking

80

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Importance of Native VLANs

81

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802.1Q Frame

82

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ISL Tagging

Performed with ASIC Not intrusive to client

stations; ISL header not seen by client

Effective between switches, and between routers and switches

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ISL trunks enable VLANs across a backbone.

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ISL Encapsulation

84

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Q & A

Q&A

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