Layer 2 and Layer 3 Switching

1
Layer 2 and Layer 3 Switching

• Freeha Khan
• 2nd Presentation
• IS 8040
• Data Communication Theory and Practice

2
Switching

• Today in data communications, all switching and
  routing equipment perform two basic operations
• Switching data frames
• Maintenance of switching operations
• Switching is the process of taking an incoming
  frame from one interface and delivering it out
  through another interface
• Routers use Layer 3 switching to route a packet,
  and switches (Layer 2 switches) use Layer 2
  switching to forward frames

3
Switches

• Switches are similar to bridges but usually have
  more ports
• Switches provide a unique network segment on each
  port, thereby separating collision domains
• Today, network designers are replacing hubs in
  their wiring closets with switches to increase
  their network performance and bandwidth while
  protecting their existing wiring investments

4
Switches

• 10/100-Mbps Ethernet Switches are good resolution
  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 dedicated 10/100
  uplinks to other switches or network backbones,
  and some even provide one or two dedicated
  Gigabit Ethernet links for especially heavy
  bandwidth requirements

5
Layer 2 Switching

• Layer 2 switches, operate at the second, or data
  link, layer of the open systems interconnection
  model

• OSI Model

6
Layer 2 Switch
Garrett Communications Magnum switches come with
eight to 24 10/100-Mbps ports and range in price
from 599 to 1,199.
7
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

8
Layer 2 Switching

• Check incoming network traffic
• Keep track of the physical addresses of all
  stations attached to their ports
• Forward traffic to specific station addresses
  according to the forwarding tables
• Layer 2 switches can deliver data at wire speeds
  because they dont have to examine individual
  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 correct
  destination
• When the frame's reply is returned, the switch
  learns the location of the new address and adds
  the information to the switching table

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Layer 3 Switching

• Layer 3 switching operates at the network layer

• OSI Model

12
Layer 3 Switch

• Limited-purpose
• Layer 3 switches are only available for Ethernet
• They only route IP/IPX protocols
• Capable to perform routing at wire speed 10,
  100, 1000 Mbps

13
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 examines packet information and forwards
  packets based on their network-layer destination
  addresses
• Layer 3 switching also supports router
  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 Switches

• The difference between Layer 2 and Layer 3
  switching is the type of information inside the
  frame that is used to determine the correct
  output interface
• With Layer 2 switching, frames are switched based
  on MAC address information
• With Layer 3 switching, frames are switched based
  on network-layer information

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Difference between Layer 2 and Layer 3 Switches

• Layer 2 switching does not look inside a packet
  for network-layer information as does layer 3
  switching
• Layer 2 switching is performed by looking at a
  destination MAC address within a frame

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Difference between Layer 2 and Layer 3 Switches

• Layer 3 switches looks at the frame's destination
  address and sends it to the appropriate interface
  if it knows the destination address location
• Layer 2 switching builds and maintains a
  switching table that keeps track of which MAC
  addresses belong to each port 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

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References

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