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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
43
Address learning Forwarding the filtering decisions Loop avoidance
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Transmitting Modes
44
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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.)
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).
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Filtering Frames
48
• Station A sends a frame to station C.
• The destination is known; the frame is not flooded.
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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.
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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.
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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
53
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
60
• 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
69
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Spanning Tree Port States
70
• Spanning tree transits each port through several different states:
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Spanning Tree Recalculation
71
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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.
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Rapid Spanning-Tree Protocol
73
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Rapid Transition to Forwarding
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Per VLAN Spanning Tree +
75
cpe@rmutt76© 2004 Cisco Systems, Inc. All rights reserved. ICND v2.2—2-76
Introducing VLAN Operations
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VLAN Overview
77
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
83
ISL trunks enable VLANs across a backbone.
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ISL Encapsulation
84
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Q & A
Q&A
85