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Network+ > Troubleshooting Ethernet Networks > Flashcards

Troubleshooting Ethernet Networks Flashcards

1
Q

Troubleshooting Methodology

A
  1. Identify Problem
  2. Establish Theory of Probably Cause
  3. Test theory to determin cause
  4. Establish Plan of action to resolve problem and identify potential effects
  5. Implement solution or escalate as necessary
  6. Verify full system functionality, and implement preventive measures
  7. Document findings, actions and outcomes
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2
Q

Idenfity Problem (Gather Informatiom)

A
  • Define scope of problem
  • Check system documentation
  • Check recent logs or records of recent work
  • Check vendor support sites
  • Identify symptoms
  • Duplicate problem, if possible
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3
Q

Identify Promblem (Question Users)

A
  • Open ended questions incite explainations in their own words: What happens when…
  • Closed call for yes/no or fixed response: What does it say… what do you see…
  • Key question: Did it ever work/when did it stop working?
  • What changed since it last worked?
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4
Q

Approach Multiple Problems Individually

A
  • You may discover symptoms of multiple problems
  • Treat them individually unless they seem related
  • Split off to separate support ticket if necessary
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5
Q

Establish Theory of Probable Cause

A
  • Use multiple approaches to determine cause
  • Question the Obivous: step through waht should happen and determine point of failure
  • Methodically prove function of each component (can be more time consuming)
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6
Q

Top-bottom vs Bottom-Top Approach

A
  • You can test at each level of OSI model in sequence
  • If it seems harward related, starting with bottom to top
  • Divide and conquer: trying to approach layer most likely causing issue.
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7
Q

Test Theory of Probable Cause

A
  • Once enough information is gathered, test to theory or escalate
  • Escalate when it is beyond your knowledge or falls in a system outside of your control
  • Escalation could also be to outside parties, like vendors
  • Provide as much information as possible to escalation point
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8
Q

Establish Plan of Action

A
  • Action plan is steps to take to solve issue
  • RepaiR: determine whether cost of repair/time to reconfigure something is best option
  • Replace: Often this is more expensive or time consuming if part is not available. Is also a possible opportunity to upgrade device or softward.
  • Ignore: Sometimes it is not worth it to fix issue if workaround is possible. Document and move on.
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9
Q

Implement Solution

A
  • Take actions to solve issue based on plan of action
  • May need to escalate.
  • If change does not solve problem, you may need to try something else.
  • Record and test after every change
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10
Q

Verify functionalist and implement preventative measures

A
  • Confirm that solution fixes issue.
  • Make sure that it didn’t cause any other issues.
  • Try to eliminate source of problem, if possible.
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11
Q

Document findings, actions and outcomes

A
  • Record information and step taken on ticket or other documentation system
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12
Q

Baud Rate

A
  • Physical layer transmission of information over channel
  • Called symbols
  • Number of symbols that can be transmitted per second, measure in hertz
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13
Q

Ethernet Speed

A
  • The expected performance of a link

- Meaured in bps

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14
Q

Throughput

A
  • Average data transfer rate achieved over a period of time
  • Included erros and other loses incurred at physical or data link laters
  • Can be affected by link distance or interferece.
  • Typically mesaured at network or transport layer
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15
Q

Latency

A
  • Speed at which packets are delivered over network
  • Measured in ms
  • Not usually a problem with local ethernets
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16
Q

Attenuation

A
  • Loss of signal strength
  • Measured in decibels (db)
  • Expresses ration of signal strength from origin to destination
17
Q

Noise

A
  • Anything that gets transmitted close or within channel that is not intended signal
  • Expressed in signal to noise ratio (SNR)
18
Q

Channel Link

A
  • Entire cable path between hose and switch port:
  • Network transceiver in the host (end system)
  • Patch able between host and wall port.
  • Structured cable between wall port and patch panel (The permanent link)
  • Patch cable between patch panel port and switch port
  • Network transceiver in switch port (intermediate system)
19
Q

Investigating Link Failure

A
  • AKA, complete loss of connectivity
  • Check patch cords are properly terminated and connected to network ports
  • Sub in good cable if necessary
  • Then test receivers, using loopback tool
  • If you can rule out bad cables and NICs/network ports, use tools to test structured cabling
20
Q

Loopback Adapter

A
  • Specially wired RJ-45 plug with 6” stub of cable
  • Wiring pinout is 1 (Tx) to pin 3 (Rx) and pin 2 (Tx) to pin 6 (Rx)
  • Packet sent by NIc is receive by itself
  • Tests bad network cards and ports
21
Q

LED Status Indicators

A
  • Check on NIC
  • May need vendor documentation to interpret LEDs
  • On switch port typically LED states are:
    Solid Green: Connected but no traffic
    Flickering Green: Operating normally with traffic
    No Light: Link is not working or disconnected at other end
    Blinking Amber: Fault has been detected (duplex mismatch or spanning tree blocking, eg.)
22
Q

Cable Tester

A
  • reports information on physical and electrical properties of the cable
  • Including Conditions, crosstalk, attenuation, noise resistance, et cetera
23
Q

TDR

A

Time Domain Reflectometer

  • May be function on cable tester
  • Measure length of cable
  • can locate open or short circuits, kinds or other problems.
  • Can give position of cable fault
24
Q

Multimeter

A
  • If cable tester or certifier is not available, multimeter can be used to verify connectivity
  • You will need to know expected results of testing electrical circuit
25
Q

Wire Map Tester

A
  • Incorporated on some multimeters or standalone device
  • Can identify following issues:
    Continuity: A conductor does not form a circle because of damage or error
    Short: Two conductors are joined at some point
    Incorrect Pinout or termination: Incorrect wiring withing cable like reversed pair or crossed pair
26
Q

Tone Generator

A
  • Used to trace a cable from one end to another

- Fox and House or tone probe

27
Q

Decible Loss

A

(db) Loss
- Represented in ration of received voltage to original
- Express logarithmically:
+3 dB means double, -3dB means halving
+6 dB means quadrupling, +6 dB means quarterin

28
Q

Crosstalk

A
  • Usually indicates bad wiring, bad connector or improper termination
  • Check cable for kinks twisting or crush points
  • Also measured in dB, but higher values represent less noise
    Types include:
    Near End (NEXT): Crosstalk on receive pairs at transmiter end, usually caused by excessive untwisting
    Attenuation to Crosstalk Ratio, Near End (ACRN): Difference between insertion loss and NEXT
    Attenuation to Crosstalk Ration, Far End(ACRF): Measured on receive pairs at recipient end.
    Power Sum:
29
Q

Straigh Though Cable

A
  • Terminated with either T568A or B at both ends

- Used for uplink ( MDI port to MDIX port)

30
Q

Crossover Cable

A
  • Terminated in T568A at one end and B at other
  • Used to connect host to host or hub to hub
  • Typically no longer necessary because of auto-MDI-MDI-X
  • All Gigabit Ethernet ports support this
31
Q

Rollover/Console Cable

A
  • Used to connect PC or laptop to command line terminal or switch or router
  • Standar RJ-45, but wired differently than ethernet
  • Modern cables use USB connector and port
  • Typically paleblue
32
Q

POE

A
  • Cat 3 or better is required for POE
  • Cat 5e or better is needed for POE+
  • Can cause heating issues
  • Shielded cabler is better at dispersing heat
33
Q

OTDR

A

Optical time Domain Reflectometer

- Sends light pulses down fiber and times reflections from break

34
Q

OSA

A

Optical Spectrum Analyzer

  • used typically with WDM to ensure each channel has sufficient power
  • At long distanced attenuation on wavelengths can vary
  • Determines whether existing cable is suitable for reuse
35
Q

Dirty Optical Cables

A
  • Dirt, dust, or grease in transmission path will reduce signal strength or block entirely
  • Most commonly on connectors
  • Connectors should be covered with dust cap when removed
  • Should be cleaned using solvent designed for fiber
  • Can also occur during splace
  • Ensure all equipment is properly cleanded
36
Q

Incorrect transceivers

A
  • Each optical interface is desnged with a specific transceiver
  • Must check specifications make sure correct fiber type is used
  • Including patch cords

Network+ (36 decks)

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