Ethernet Frame

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• Ethernet Frame

Preamble
Destination Address
Source Address
Length/ Type
LLC/ Data
Frame Check Sequence
2

• Ethernet Addresses

• 48 bit
• normally shown in HEX
• e.g. 02-60-8C-44-59-E0
• first 24 bits are obtained from IEEE by hardware
  manufacturers
• one bit is used to distinguish unicast from
  multicast addresses
• one bit is used to distinguish locally assigned
  addresses(rare) from globally assigned addresses
  (typical)

3

• Transmission Types

• Unicast - intended for one specific station
• Broadcast - intended for all stations
• Multicast - intended for a group of stations

4

• CSMA/CD

• Carrier Sense, Multiple Access with Collision
  Detection
• Carrier sense - don't transmit if there is
  already a signal
• Collision detection - if a collision is detected
  jam, wait, and retransmit

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• No Carrier

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• Transmission

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• Transmission

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• End of Transmission

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• Transmission

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• Second Transmission

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• Collision

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• Collision detected

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• Wait

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Ethernet HUB(repeater)

• Layer 1 device
• Repeat signal on all ports
• Enforce collision on all segments (jam)
• Restore amplitude of the signal
• Retime the signal
• Single speed
• May mix media

16

• Repeater Hub

17

• Repeater Hub
• one station transmits

18

• Repeater Hub
• signal repeated on all other ports

19

• Repeater Hub
• signal repeated on all other ports

20

• Repeater Hub
• end of transmission

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• Repeater Hub

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Matrix Module
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Collision Domain

• Devices connected by hubs
• Only one device can transmit at a time
• Collisions detected by all devices in the domain

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One Collision Domain
Hub
Hub
Hub
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Broadcast Domain

• Devices connected by switches
• Can contain multiple collision domains
• One transmission in each collision domain
• Collisions do not propagate between collision
  domains
• Broadcast frames do propagate to all collision
  domains
• Can be full duplex if only two devices in
  collision domain and both devices are full duplex
  cabable

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Three Collision Domains One Broadcast Domain
Switch
Hub
Hub
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H Ethernet Hub S Ethernet Switch R IP
Router W Workstation _____ Ethernet Segment
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H Ethernet Hub S Ethernet Switch R IP
Router W Workstation _____ Ethernet Segment
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H Ethernet Hub S Ethernet Switch R IP
Router W Workstation _____ Ethernet Segment
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H Ethernet Hub S Ethernet Switch R IP
Router W Workstation _____ Ethernet Segment
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Ethernet switch

• Function (old name) bridge
• Forwards or Filters unicasts
• Floods (forwards to all ports) all broadcasts
• Learns address locations
• Can be full duplex if only two devices in
  collision domain and both devices are full duplex
  cabable
• Can mix speeds and media

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DA SA Action
FF E2
E2 E3
E3 E2
FF E5
E5 E6
E6 E5
E4 E1

ADDRESS PORT






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Switch Light Videos

• Switch Lights(3.5 MB)
• Switch Lights more(5.9 MB)

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Cut-Through Mode andStore and Forward Mode

• Cut-through mode
• Switching mode in which switch reads a frames
  header and decides where to forward the data
  before it receives the entire packet
• Can detect runts, or packet fragments
• Store and forward mode
• Switching mode in which switch reads the entire
  data frame into its memory and checks it for
  accuracy before transmitting it

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Using Switches to Create VLANs

• Virtual local area networks (VLANs)
• Means by which a switch can logically group a
  number of ports into a broadcast domain
• Broadcast domain
• Combination of ports that make up a Layer 2
  segment and must be connected to a Layer 3 device

FIGURE 6-24 Simple VLAN design
44
Trunk Aggregation
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Resilient Links
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Higher-Layer Switches

• Switch capable of interpreting Layer 3 is called
  a Layer 3 switch
• Switch capable of interpreting Layer 4 is called
  a Layer 4 switch
• Higher-layer switches may also be called routing
  switches or application switches

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Routers

• Multiport device
• Can connect dissimilar LANs and WANs running at
  different transmission speeds and using a variety
  of protocols

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Router Features and Functions

• Filter out broadcast transmission to alleviate
  network congestion
• Prevent certain types of traffic from getting to
  a network
• Support simultaneous local and remote activity
• Provide high network fault tolerance through
  redundant components
• Monitor network traffic and report statistics to
  a MIB
• Diagnose internal or other connectivity problems
  and trigger alarms

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Routers
FIGURE 6-26 Placement of routers on a LAN
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Routing Protocols

• Means by which routers communicate with each
  other about network status
• Convergence time
• The time it takes for a router to recognize a
  best path in the event of a change or outage
• Bandwidth overhead
• Burden placed on an underlying network to support
  the routing protocol

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Routing Protocols

• RIP (Routing Information Protocol) for IP and IPX
• OSPF (Open Shortest Path First) for IP
• Best path refers to the most efficient route from
  one node on a network to another
• EIGRP (Enhanced Interior Gateway Routing
  Protocol) for IP, IPX, and AppleTalk
• BGP (Border Gateway Protocol) for IP

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Gateways

• Combination of networking hardware and software
  that connects two dissimilar kinds of networks
• E-mail gateway
• IBM host gateway
• Internet gateway
• LAN gateway