Switching Technologies

7/30/2019 Switching Technologies

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Understanding LAN

Switching


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Agenda

Shared LAN Technology

LAN Switching Basics

Key Switching

Technologies


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Shared LAN Technology


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Early Local Area Networks

Thick Ethernet Limited to 500 meters before signal degradation

Required repeaters every 500 meters

Limitations on number and placement of stations

Expensive, large, and difficult to pull through buildings Relatively simple to add new users

Provided 10-Mbps shared bandwidth

Thin Ethernet

Less expensive and required less space than thick Ethernet Still difficult to pull through buildings

Adding users required network interruptions


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Hubs Addressed Many of

These Problems

Ethernet 10

One device sending at a time

Hub

All nodes share 10 Mbps

Ethernet concentrator

Self-contained EthernetLAN in a box

Passive

Works at physical layer 1


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Collisions: Telltale Signs

Sluggish network response

Increasing user complaints

CRASH

Hub

I could have walked to

Finance by now.

I knew I should have

stayed home.

File transfers take

forever.

Im waiting all the time.


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Other Bandwidth Consumers

Unicast

Broadcast

Multicast


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Apple

TCP/IP

Broadcasts Consume Bandwidth

Resolve addresses

Distribute route information

Find network services


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Broadcasts Consume Processor

Performance

Broadcasts and multicasts interrupt

all computers on the network

Broadcasts/Second

CPU %

1 0 0 1 0 0 0 3 0 0 0

0

1 0

2 0

3 04 0

5 0

6 0

7 0

8 0

1 0 0 1 0 0 0 3 0 0 0

SPA R C 2

SPA R C 5

Pe nt i um 12 0 MH z


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Hub-Based LANs

Shared resources

Desktop connections wired tocentralized closets

Poor security within shared

segments Routers provide scalability

Adds, moves, and changes areeasier than without hubs, butstill a hassle

Groups of users determined byphysical location

10BaseTHub

10BaseTHub


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Bridges

More intelligent than a hub

Eavesdrop on conversations tolearn and maintain address tables

Collect and pass packets betweentwo network segments

Control traffic to the network

Bridge

Segment 1 Segment 2

123

124

125

126

127

128

Corporate Intranet

Hub Hub


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SwitchesLayer 2

EthernetSwitch

Each Node has10 Mbps

BackboneSwitched Ethernet 10

Multiple devices sending at the same time


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Switches versus Hubs

Ethernet 10One devicesending at

a time

Hub

All nodes share 10 Mbps

EthernetSwitch

Each node has 10 Mbps

Backbone Switched Ethernet 10

Multiple

devicessending at thesame time


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SLOW

The Need for Speed:

Early Warning Signs

File transfers take forever

You can take a coffee break

between screen refreshes

Network print jobs: same-

day service?

Multimedia applications

SLOW

Mbps


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Typical Causes of Network

Congestion Too many users on a

10-Mbps segment

Most users accessingone or two servers

High-performance

PCs such as EISA,PCI, and S-Bus

Network-intensiveapplications suchas color publishing,CAD/CAM, imaging,

and relationaldatabases

File Transfer Client/Server Image

Processing

Backup/Mng Transaction

Processing

E-Mail Desktop Video

Traditional DataRequirements Drive LAN

Bandwidth

BandwidthRequirements


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Network Traffic Impact from

Centralization of Servers

Servers are gradually moving into a central area

(data center) versus being located throughout the company to:

Ensure company data integrity

Maintain the network and ensure operability

Maintain security

Perform configuration and administrative functions

More centralized servers increase the bandwidth

demands on campus and workgroup backbones

Servers inWiring Closets

RandomlyDistributed

Servers

CentralizedServers inData Center

MainframeData Center


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Todays LANs

Mostly switched

resources; few

shared

Routers provide

scalability

Groups of usersdetermined by

physical location

10/100Switch

10-Mbps

Hub

10/100Switch


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Enables dedicated

access

Eliminates collisionsand increases

capacity

Supports multipleconversations at the

same time


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A C

B

2

4

1

10 Mbps

10 Mbps

LAN Switch Operation

Forwards packets based ona forwarding table Forwards based on the MAC

(Layer 2) address

Operates at OSI Layer 2

Learns a stations locationby examining sourceaddress Sends out all ports when

destination address isbroadcast, multicast, orunknown address

Forwards when destination islocated on different interface

Interface

Stations

1 2 3 4

3Data from A to B


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A C

B

2

4

1

10 Mbps

10 Mbps



(Layer 2) address





Interface

Stations

1 2 3 4

A X

3


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A C

B

2

4

1

10 Mbps

10 Mbps



(Layer 2) address





Interface

Stations

1 2 3 4

A X

3Data from A to B

DatafromAtoB

DatafromA

toB


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A C

B

2

4

1

10 Mbps

10 Mbps



(Layer 2) address





Interface

Stations

1 2 3 4

A X

3

B X

DatafromB

toA


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A C

B

2

4

1

10 Mbps

10 Mbps



(Layer 2) address





Interface

Stations

1 2 3 4

A X

B X

3

Data from B to A


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Switching Technology: Full

Duplex

Doubles bandwidth between nodes

e.g. switch and server

Collision-free transmission

Two 10- or 100-Mbps data paths

Full Duplex Switch

10 or 100 Mbps

10 or 100 Mbps

10 or 100 Mbps

10 or 100 Mbps


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Key Switching Technologies


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Key Switching Technologies

802.1d Spanning-Tree Protocol

Multicasting


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Problems with large switched networks

Local multicast, broadcast, and unknown single-destinationevent storms become global events

The Need for Spanning Tree

Station A

Station B

Segment A

Segment B

Switch 1 Switch 2

1/1

1/2

2/1

2/2


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802.1d Spanning-Tree

Protocol (STP) Allows redundancy by using parallel links

Shuts down redundant links to eliminateloops

Switches communicate with each otherusing BPDUs (Bridge Protocol Data Units)

Takes 3060 seconds to converge

Cisco refinements: PortFast

UplinkFast


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Multicasting

Emerging applicationsrequire increasedbandwidth

E-mail, file transfers, andfile sharing are easy tohandle

Emerging applications arebandwidth hungry

Multipoint communicationsare required Simultaneous communication between

groups of computers

Video

LAN TV

Desktopconferencing

Corporatebroadcasts

Collaborativecomputing


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Multipoint Communications

Broadcast Applications address each packet to a single

broadcast address

Packets are broadcast to every station

Multicast

Applications address each packet to a group of receivers Network forwards the packets to only the networks

that need to receive them


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WAN

VideoServers

Channel 1

Channel 2

Channel 3

1

2

3

Multicast

Internet Group Management

Protocol (IGMP)

Multicast routing protocols

IGMPMulticast RoutingProtocols

Switches typically flood allports with multicast traffic

Problem: How toprevent multicastingflooding?


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WAN

VideoServers

Channel 1

Channel 2

Channel 3

1

2

3

End-to-End Multicast


Protocol (IGMP)


IGMP

Cisco Group Management

Protocol (CGMP)

CGMP

Wire-SpeedMulticast

Multicast RoutingProtocols


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VideoServers

Channel 1

Channel 2

Channel 3

1

2

3

End-to-End Multicast

IGMP


Protocol (IGMP)


Cisco Group Management

Protocol (CGMP)

WAN

CGMP

Wire-SpeedMulticast

Multicast RoutingProtocols


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Why Use Multicast?

1 20 40 60 80 100

Number of Clients

0.8

0.6

0.4

0.2

0

TrafficMbps With multicast

Without multicast

100-kbps Video Stream

Highly scalable information delivery


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Summary

Switches provide dedicated access

Switches eliminate collisions and increasecapacity

Switches support multiple conversations atthe same time

Switches provide intelligence for

multicasting


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Are Switches A Commodity?

Not if the customer understands thevalue of an end-to-end solution

Cisco IOS throughout the network offers: Guaranteed interoperabilityend-to-end

One number to call for supportno finger pointing

Enhanced network servicesend-to-end

Higher performance

Quality of Service

Reliability

Reduced cost for network administration

The promise of policy-based management


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Virtual Private Networks extend the classic WAN VPNs leverage the classic WAN infrastructure, including Ciscos

family of VPN-enabled routers and policy management tools

VPNs provide connectivity on a shared infrastructurewith the same policies and performance as a privatenetwork with lower total cost of ownership

Service ProviderShared

Network

VPN

Internet, IP, FR, ATM

What Are VPNs?

Documents

Switching Technologies