Click to edit Master subtitle style Chapter 19: Network Troubleshooting Click to edit Master subtitle style

Chapter 19 Objectives The Following CompTIA Network+ Exam Objectives Are Covered in This Chapter: 4.1 Given a scenario, implement the following network troubleshooting methodology • Identify the problem o Gather information o Duplicate the problem, if possible o Question users o Identify symptoms o Determine if anything has changed o Approach multiple problems individually • Establish a theory of probable cause o Question the obvious o Consider multiple approaches - Top-to-bottom/bottom-to-top OSI model - Divide and conquer 2

Chapter 19 Objectives (cont) • Test the theory to determine cause o Once theory is confirmed, determine next steps to resolve problem o If theory is not confirmed, re-establish new theory or escalate • Establish a plan of action to resolve the problem and identify potential effects • Implement the solution or escalate as necessary • Verify full system functionality and if applicable implement preventative measures • Document findings, actions, and outcomes 3

Chapter 19 Objectives (cont) 4.3 Given a scenario, troubleshoot and resolve common wireless issues • Signal loss • Interference • Overlapping channels o Mismatched channels • Signal-to-noise ratio • Device saturation • Bandwidth saturation • Untested updates • Wrong SSID • Power levels • Wrong antenna type • Incompatibilities • Wrong encryption • Bounce • Environmental factors o Concrete walls o Window film o Metal studs • Wireless standard related issues o Throughput o Frequency o Distance o Channels 4

Chapter 19 Objectives (cont) 4.4 Given a scenario, troubleshoot and resolve common copper cable issues • Shorts • Opens • Incorrect termination (mismatched standards) o Straight-through o Crossover • Cross-talk o Near end o Far end • EMI/RFI • Distance limitations • Attenuation/Db loss • Bad connector • Bad wiring • Split pairs 5

Chapter 19 Objectives (cont) • Tx/Rx reverse • Cable placement • Bad SFP/GBIC - cable or transceiver 4.5 Given a scenario, troubleshoot and resolve common fiber cable issues • Attenuation/Db loss • SFP/GBIC - cable mismatch • Wavelength mismatch • Fiber type mismatch • Dirty connectors • Connector mismatch • Bend radius limitations • Distance limitations 6

Chapter 19 Objectives (cont) 4.6 Given a scenario, troubleshoot and resolve common network issues • Incorrect IP configuration/default gateway • Broadcast storms/switching loop • Duplicate IP • Speed and duplex mismatch • End-to-end connectivity • Incorrect VLAN assignment • Hardware failure • Misconfigured DHCP • Misconfigured DNS • Incorrect interface/interface misconfiguration • Cable placement • Interface errors • Simultaneous wired/wireless connections • Discovering neighboring devices/nodes • Power failure/power anomalies • MTU/MTU black hole • Missing IP routes • NIC teaming misconfiguration o Active-active vs active-passive o Multicast vs broadcast 7

Network Troubleshooting Troubleshooting computers and networks is a combination of art and science, and the only way to get really good at it is by doing it. Check quickly for problems in the “super-simple stuff” category. Move to common troubleshooting models that you can use like a checklist to go through to solve a surprising number of network problems. 8

Narrowing Down the Problem Did You Check the Super Simple Stuff? Check to ensure login procedures and rights. Look for link lights and collision lights. Check all power switches, cords, and adapters. Look for user errors. Are There Any Cabling Issues? 9

Narrowing Down the Problem Correct Login Procedure and Rights Username and password is being entered correctly? Check that Caps Lock key. Can the Problem Be Reproduced? The Link and Collision Lights The Power Switch Operator Error 10

Narrowing Down the Problem Is Hardware or Software Causing the Problem? Is It a Workstation or a Server Problem? Which Segments of the Network Are Affected? Is It Bad Cabling or Cabling issues? Crosstalk Near-End or Far-end crosstalk Attenuation Collisions Shorts Open impedance mismatch (echo) Interference 11

Narrowing Down the Problem Unbounded Media Issues (Wireless) Interference Incorrect encryption Incorrect channel Incorrect frequency ESSID mismatch Standard mismatch Distance Bounce Incorrect antenna placement 12

Troubleshooting Steps Step 1: Identify the Problem Question Users Determine If Anything Has Changed Identify Symptoms 13

Troubleshooting Steps Step 2: Establish a Theory of Probable Cause Question the Obvious Port speed Port duplex mismatch Mismatched MTU Incorrect VLAN Incorrect IP address Wrong gateway Wrong DNS Wrong subnet mask 14

Troubleshooting Steps Step 3: Test the Theory to Determine Cause 15

Troubleshooting Steps Step 4: Establish a Plan of Action to Resolve the Problem and Identify Potential Effects

Troubleshooting Steps Step 5: Implement the Solution or Escalate as Necessary Some of the calamities that you should escalate are as follows: Switching loops Missing routes Routing loops Routing problems MTU black hole Bad modules Proxy Address Resolution Protocol (ARP) Broadcast storms 17

Troubleshooting Steps Step 6: Verify Full System Functionality and If Applicable Implement Preventative Measures Step 7: Document Findings, Actions, and Outcomes A description of the conditions surrounding the problem The OS version, the software version, the type of computer, and the type of NIC Whether you were able to reproduce the problem The solutions you tried The ultimate solution 18

Troubleshooting Tips Don’t Overlook the Small Stuff Prioritize Your Problems Check the Software Configuration Don’t Overlook Physical Conditions Don’t Overlook Cable Problems Check for Viruses 19

Troubleshooting Steps Review 1. Identify the problem. 2. Establish a theory of probable cause. 3. Test the theory to determine cause. 4. Establish a plan of action to resolve the problem and identify potential effects. 5. Implement the solution or escalate as necessary. 6. Verify full system functionality and if applicable implement preventative measures. 7. Document findings, actions, and outcomes. 20

Summary Summary Exam Essentials Section Written Labs Review Questions 21