Transcript Meyers_CompTIA_4e_PPT_Ch04x

Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Ethernet Basics
Chapter 4
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Objectives
• Define and describe Ethernet
• Explain early Ethernet implementations
• Describe ways to extend and enhance
Ethernet networks
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Introduction
• Networks did not exist when computers were
first created
– Sneakernet was the method of moving files
– A more efficient method of sharing data was
developed
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Historical/Conceptual
Ethernet
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
The First Ethernet Implementation
•
•
•
•
•
Developed by Xerox in 1973
Based on bus topology
Transferred data at 3Mbps max
Remained in-house technology until 1979
Evolved into today’s Ethernet standards
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
The Next Iteration of the Ethernet
• DIX (Digital-Intel-Xerox) standard
– Transferred data at 10Mbps max
• DEC, Intel, and Xerox transferred control of the
Ethernet standard to IEEE
– 802.3 (Ethernet) committee
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Issues Faced by Ethernet’s Designers
• How to send data across the wire
• How to identify the sending and receiving
computers
• How to determine which computer should use
shared cable at what time
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Topology
• Hybrid star-bus
• Hub at the center
– Electronic repeater
– Repeats the same signal out to the other
connected ports
– Does not send signal back down the
originating port
– Repeaters are not amplifiers
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 4.1 Ethernet hub
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Test Specific
Organizing the Data:
Ethernet Frames
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Ethernet Frames
• Smaller pieces of data transmitted between
computers
• Using frames addresses two networking issues
– Prevents any single machine from monopolizing
the shared bus cable
– Makes retransmitting lost data more efficient
• Used by all networking technologies (including
Ethernet)
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 4.2 Ethernet frame
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Preamble and MAC addresses
• Preamble
– Beginning of each frame
– Seven bytes of alternating ones and zeros
• Start frame
– Follows the preamble
– One byte
• MAC address
– Unique identifying address for each node
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 4.3 Frames propagating on a network
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
NICs
• Ethernet security vulnerability
– Sniffers can order a NIC to run in promiscuous
mode
• NIC processes all frames, not only those intended for its
MAC address
– Sniffers have legitimate uses, but may also be
used unscrupulously
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Type and Data
• Type
– Helps receiving computer interpret the frame
contents at a basic level ►IPv4 or IPv6 data
• Data
– Part of the frame that contains the payload
– If an IP packet, packet contains extra information
such as the IP addresses of both systems
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Pad and the Frame Check Sequence
• Pad
– Minimum Ethernet frame size is 64 bytes
– Extra data added if frame has fewer than 64 bytes
• Frame check sequence
– Aids in determining if the data has been damaged
in transit
– Calculation used at the beginning and at the end
of transmission must give same result
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Network Access
• Carrier sense
– Each node checks to see whether cable is in use
– Sends the frame when cable is free
• Multiple access
– All machines have equal access to the wire
– Collision occurs if two machines send frame
simultaneously
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
CSMA/CD
Carrier Sense
Each NIC on the network
examines the wire before
sending a frame. If the
node detects traffic, it will
pause a random amount
of time and try again.
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Multiple Access
All machines have
equal access to the
wire. Access to the
wire is on a firstcome, first-served
basis
Collision Detection
If two NICs transmit at
the same time, a
collision results. NICs
may listen to detect a
collision.
Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 4.4 No one else is talking—send the frame!
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 4.5 Collision!
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Collisions
• When collision occurs
– Both machines generate a random number to
determine delay time before resending packet
• Properly running Ethernet network has a
maximum collision rate of 10 percent
• Collision domain
– A group of nodes that could send frames at the
same time ►could potentially cause a collision
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 4.6 Rolling for timing
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Early Ethernet Networks
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Bus Ethernet
• Original Ethernet networks used a true bus
topology
• Thicknet (10Base5)
• Thinnet (10Base2)
– The T connector enabled the bus to carry a single
electrical signal that connected every device on
the network
• The ends of the bus have to be terminated
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 4.7 Thicknet vampire tap
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 4.8 10Base2 T connector in action
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 4.9 Terminating resistor
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
10BaseT: Physical vs. Logical
• Over 99 percent of all networks use 10BaseT
or its newer versions
• Consists of two or more computers connected
to a central hub
• NICs connect with wires per 802.3 standards
• Hubs for 10BaseT
– Vary in size, shape, and number of ports
– All need electrical power
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
10BaseT
Speed
10 Mbps
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Signal Type
Baseband
A single signal
on the cable
Type of cable
Twisted Pair
Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 4.10 Two 10BaseT hubs
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
10BaseT: UTP
• Uses CAT 3 or higher
• Two pairs of wires required (four-pair cable
commonly used)
• One pair of wires sends data to the hub
• The other pair receives data from the hub
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 4.11 A typical four-pair CAT 5e unshielded
twisted-pair cable
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Check Your CATS!
• RJ-45 Connector
– Used in 10BaseT
– Each pin connects to a single wire inside the cable
– Pins are numbered from one to eight
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 4.12 Two views of an RJ-45 connector
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 4.13 The pins on an RJ-45 connector are
numbered 1 through 8
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Check Your CATS! (cont’d.)
• RJ-45 pin assignments
– 1 and 2 send data
– 3 and 6 receive data
– Duplex versus half-duplex mode
• RJ-45 connector is called a crimp
– Crimping is the act of installing an RJ-45 connector
– A crimper is the tool used
• Wires are color-coded
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 4.14 Color-coded pairs
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
TIA/EIA 568A and 568B
• TIA/EIA defines industry standards for correct
crimping
• Advantage of following an established color
code scheme
– Ensures wires match up correctly at each end
of the cable
• Network technicians can make their own
Ethernet cables
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 4.15 The TIA/EIA 568A and 568B standards
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
10BaseT Limits and Specifications
• Maximum distance between hub and
computer: 100 meters
• No more than 1024 computers connected
to one hub
– Such a high number is too expensive and not
practical
– Excessive collisions can easily bog down Ethernet
performance
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
10BaseT Summary
•
•
•
•
•
Speed:
Signal type:
Distance:
Node limit:
Topology:
• Cable type:
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10 Mbps
Baseband
100 meters between hub/node
1024 nodes per hub
Star-bus topology: physical star,
logical bus
CAT3 or better UTP cabling with
RJ-45 connectors
Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
10BaseFL
• Fiber-optic version
• Increased maximum distance
– Two kilometers between the hub and the node
• Immune to electrical interference
• More secure because difficult to tap into
• Multimode fiber-optic cables with ST or SC
connectors
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 4.16 Typical 10BaseFL card
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
10BaseFL Summary
•
•
•
•
•
Speed:
Signal type:
Distance:
Node limit:
Topology:
• Cable type:
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10Mbps
Baseband
2000 meters between hub/node
1024 nodes per hub
Star-bus topology: physical star,
logical bus
Multimode fiber-optic cabling with
ST or SC connectors
Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Media Converters
• 10BaseT and 10BaseFL have different cabling
and hubs but same Ethernet packets
• A media converter connects different Ethernet
types
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 4.17 Typical copper-to-fiber Ethernet media converter
(photo courtesy of TRENDnet)
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Extending and Enhancing
Ethernet Networks
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
General Tips
• Install additional hubs to connect multiple
LANs
• Use a network bridge to connect two Ethernet
networks
• Replace hubs with better devices to reduce
collisions
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Coupler
• Device with female connectors on both ends
• Used to connect a machine in a location not
planned for in original network
• Examples of coupler types
– BNC couplers
– UTP couplers
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Connecting Ethernet Segments
• When all ports on an existing hub have been
used, add another hub or a bridge
– Hubs can be connected using an uplink port or
a crossover cable
• Uplink ports
– Connect two hubs using a straight-through cable
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 4.19 Typical uplink port
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Connecting Hubs
• When connecting hubs:
– You can only daisy-chain hubs
– Take time to figure out the uplink ports
– If you plug hubs in incorrectly, no damage will
occur (they just won’t work)
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 4.20 Daisy-chained hubs
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 4.21 A hierarchical hub configuration will not work!
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 4.22 Press-button port
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Crossover Cables
• Another way to connect two hubs
• Connect via two normal ports using one
crossover cable
• Reverse sending and receiving pairs on
one end
– One end crimped per TIA/EIA 568A
– Second end crimped per TIA/EIA 568B
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 4.23 A crossover cable reverses the sending and
receiving pairs
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Bridge
• Acts like a repeater or hub to connect two
Ethernet segments
• Goes one step beyond a repeater or hub
– Filters and forwards traffic
• At first, acts like a repeater or hub
• Monitors and records network traffic
– Then begins to filter and forward
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Switched Ethernet
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
The Trouble with Hubs
• Classic 10BaseT network can only have one
message on the wire at a time
• Collisions slow the effective transmission
speed for the whole network
• Ethernet switch
– Creates point-to-point connections between two
conversing computers
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 4.24 Hub (top) and switch (bottom) comparison
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Switches to the Rescue
• Ethernet switches give every conversation the
full bandwidth of the network
• Source Address Table (SAT)
– A switch copies the source MAC addresses and
builds a table of MAC addresses of each
connected computer
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 4.25 A switch tracking MAC addresses
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 4.26 A switch making two separate connections
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 4.27 Switches are very commonly connected in a tree
organization
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Spanning Tree Protocol (STP)
• Eliminates the problem of accidental bridge
loops (i.e., redundant connections in a
network)
• With STP enabled:
– Loops are detected
– Looped port’s state is set to blocking
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Figure 4.28 A bridging loop
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Spanning Tree Protocol (cont’d.)
• STP-enabled switches use a Bridge Protocol
Data Unit (BPDU) frame
– Determines distance between them
– Helps keep track of changes on the network
• Rapid Spanning Tree Protocol (RSTP), 802.1w
replaced the original STP in 2001
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Mike Meyers’ CompTIA Network+® Guide to Managing and
Troubleshooting Networks, Fourth Edition (Exam N10-006)
Troubleshooting Hubs and Switches
• Problem categories
– Physical damage, dead ports, or general flakiness
• Hub or switch might have problems if device
can’t connect to the network
• Check for link lights
• Check cables
• Replace hub or switch with a known-good
device
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