Switching (Layer 2 and Layer 3 Switching)

7/30/2019 Switching (Layer 2 and Layer 3 Switching)

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Layer 2 and Layer 3 Switching

Freeha Khan

2nd PresentationIS 8040

Data Communication Theory and Practice


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Switching

Today in data communications, all switchingand routing equipment perform two basicoperations:

Switching data frames Maintenance of switching operations

Switching is the process of taking anincoming frame from one interface and

delivering it out through another interfaceRouters use Layer 3 switching to route apacket, and switches (Layer 2 switches) useLayer 2 switching to forward frames


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Switches

Switches are similar to bridges but usuallyhave more ports

Switches provide a unique network segmenton each port, thereby separating collisiondomains

Today, network designers are replacing hubs

in their wiring closets with switches toincrease their network performance andbandwidth while protecting their existingwiring investments


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Switches

10/100-Mbps Ethernet Switches are goodresolution if Ethernet LANs are stretched to

the breaking point under the weight of new users, servers and high-end applications

Most switches provide shared or dedicated10/100 uplinks to other switches or network

backbones, and some even provide one ortwo dedicated Gigabit Ethernet links forespecially heavy bandwidth requirements


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Layer 2 Switching

Layer 2 switches,operate at the

second, or data link,layer of the opensystemsinterconnection

model

OSI Model

Application

Presentation

Session

Transport

Network

Data Link

Physical


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Layer 2 Switch

Garrett Communications Magnum switchescome with eight to 24 10/100-Mbps ports andrange in price from $599 to $1,199.


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Layer 2 Switching

Layer 2 switches operate at MAC layer

Layer 2 switches broadcast multicast traffic to all

their ports

very detrimental to performance

Static entries can be defined on switches to

control multicast at layer 2 but static entries do

not react to dynamic behaviors


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Layer 2 Switching

Check incoming network traffic

Keep track of the physical addresses of all

stations attached to their portsForward traffic to specific station addressesaccording to the forwarding tables

Layer 2 switches can deliver data at wirespeeds because they dont have to examineindividual data packets


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Layer 2 Switching

Flow of intersubnet traffic with Layer 2 switches and

routers


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Layer 2 Switching

If the Layer 2 switch does not know where to

send the frame, it broadcasts the frame out all its

ports to the network to learn the correctdestination

When the frame's reply is returned, the switch

learns the location of the new address and addsthe information to the switching table


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Layer 3 Switching

Layer 3 switchingoperates at the

network layer

OSI Model

Application

Presentation

Session

Transport

NetworkData Link

Physical


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Layer 3 Switch

Limited-purpose

Layer 3 switches are only available forEthernet

They only route IP/IPX protocols

Capable to perform routing at wirespeed: 10, 100, 1000 Mbps


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Layer 3 Switching

Hardware based packet-to-packet IP

routing

Hardware based routers cost less than

traditional software-based routers

They switch non-routable traffic to Layer 2


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Layer 3 Switch

RapierTM 10/100 Layer 3 Switch


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Layer 3 Switching

It examinespacketinformation andforwards packets based on their

network-layer destination addresses

Layer 3 switching also supportsrouter functionality


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Layer 3 Switching

Flow of intersubnet traffic with Layer 3 switches


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Difference between Layer 2 and

Layer 3 SwitchesThe difference between Layer 2 and Layer 3switching is the type of information inside the

frame that is used to determine the correctoutput interface

With Layer 2 switching, frames are switchedbased on MAC address information

With Layer 3 switching, frames are switchedbased on network-layer information


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Layer 3 SwitchesLayer 2 switching does not lookinside a packet for network-layer

information as does layer 3switching

Layer 2 switching is performed by

looking at a destination MACaddress within a frame


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Layer 3 SwitchesLayer 3 switches looks at the frame'sdestination address and sends it to the

appropriate interface if it knows thedestination address location

Layer 2 switching builds and maintains

a switching table that keeps track ofwhich MAC addresses belong to eachport or interface


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References

Switched, Fast, and Gigabit Ethernet, Robert

Breyer and Sean Riley, Third Edition

Business Data Communications, Stallings,Fourth Edition

http://www.gcn.com

http://www.slac.stanford.edu/

http://www.cisco.com/univercd
http://www.gcn.com/http://www.slac.stanford.edu/http://www.cisco.com/univercdhttp://www.cisco.com/univercdhttp://www.slac.stanford.edu/http://www.gcn.com/


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References

http://www.gcn.com/state/vol6_no9/guide/837-

2.html

http://www.msic.com
http://www.gcn.com/state/vol6_no9/guide/837-2.htmlhttp://www.gcn.com/state/vol6_no9/guide/837-2.htmlhttp://www.msic.com/http://www.msic.com/http://www.gcn.com/state/vol6_no9/guide/837-2.htmlhttp://www.gcn.com/state/vol6_no9/guide/837-2.htmlhttp://www.gcn.com/state/vol6_no9/guide/837-2.html

Switching (Layer 2 and Layer 3 Switching)

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