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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)
Transmission Types
Unicast - intended for one specific station Broadcast - intended for all stations Multicast - intended for a group of stations
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
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
Collision Domain
• Devices connected by hubs
• Only one device can transmit at a time
• Collisions detected by all devices in the domain
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
H – Ethernet Hub
S – Ethernet Switch
R – IP Router
W – Workstation
_____ Ethernet Segment
R
S
H
W
S
S
H
H
W
W
H
W WW
W WW
H – Ethernet Hub
S – Ethernet Switch
R – IP Router
W – Workstation
_____ Ethernet Segment
R
S
H
W
S
S
H
H
W
W
H
W WW
W WW
H – Ethernet Hub
S – Ethernet Switch
R – IP Router
W – Workstation
_____ Ethernet Segment
R
S
H
W
S
S
H
H
W
W
H
W WW
W WW
H – Ethernet Hub
S – Ethernet Switch
R – IP Router
W – Workstation
_____ Ethernet Segment
R
S
H
W
S
S
H
H
W
W
H
W WW
W WW
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
switch
HubHubHub
E1 E2 E3 E4 E5 E6
1 2 3
DA SA Action
FF E2
E2 E3
E3 E2
FF E5
E5 E6
E6 E5
E4 E1
ADDRESS PORT
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Cut-Through Mode andStore and Forward Mode
• Cut-through mode– Switching mode in which switch reads a frame’s 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
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
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
Routers
• Multiport device• Can connect dissimilar LANs and WANs running
at different transmission speeds and using a variety of protocols
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
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
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