# Explain Network Troubleshooting Methodology Links: [[TroubleShooting Methodology]], [[Deploying Ethernet Cabling]], [[Deploy Ethernet Switching]] 1) Identify problem - Determing Scope (who/what) 2) Establish theory of probably cause/question the obvious 3) Test theory to determine cause 4) Establish action plan 5) Implement solution or escalate 6) Verify FULL system functionality 7) Implement preventative measures 8) Perform root cause analysis 9) Document findings, actions, and outcomes ip address of 169.xxx.xxx.xxx is the default microsoft IP address. YOU ARE NOT CONNECTED TO ANYTHING. It means something went wrong. **Tips for establishing a theory or probable cause** - Question the obvious - Prove functionality systematically - OSI MODEL approach... - Layer-by-layer - Top-to-bottom - Bottom-to-top - Divide and conquer **Test the theory to determine the cause** - isolate the issue to a component or system - Run tests to prove the theory - Escalate if necessary - too difficult - warrenty/supplier issue - scope too large - customer issues **Establish a plan of action** - typical solutions... - repair - replace - ignore - Plan changes carefully - try to anticipate effects **Verify system is fully functional** - consider impact on overall system functionality - test that the problem is fixed AND it functions normally - identify preventive measures to prevent from recurring # Troubleshoot Common Cable Connectivity Issues learn the Specification vs Limitations for media and hardware... ## Cable Issues - Channel link - End system transceiver > patch cord - Permenant link wall port > patch panel - Patch cord > intermediate system port - Test each component - Known good patch cords - port tester - structered cabling test tools ## Loopback adapter plugs, status indicators, interface config - loopback adapter/plug - tests the port by transmitting to itself - status indicators - LEDs on NIC and switch port - Interface configuration - check for static config on switch port ## Cable Testers - Verify you are using the correct cable category for the application (bandwidth, length, PoE) - Consider whether screened/shielded cable is required or even plenum cable - Use a cable tester to report detailed characteristics of the link - Use a **t**ime **d**omain **r**eflectometer (TDR) to measure length and locate installation problems or faults ## Wire Map Testers and Tone Generators - Multimeter - continuity - Wire map tester - check pinouts are correct - opens and shorts - Reversed, crossed, and split pairs - Tone generator - trace cable path. Very helpful if the machines arent labled with what port it is using on the switch - identify cable within a bundle ## Attenuation and Interference Issues - Attenutation - be certain of limitations of media and hardware - reduces link speed and causes errors and retransmissions - Measure using cable certifier and compare to tolerance for cable category - dB insertion loss (signal is too weak at the destination) - can use repeaters for example to fix problem - Ratio of input to output using logarithms - dBm is the ration to 1 mw - Absolute value (smaller better) versus margin (larget better) - Interference - cable placement and electromagnetic interference (EMI) sources - Alien crosstalk - cables next to eachother that arent shielded ## Crosstalk issues - Interference within cable due to faulty wiring or termination - Near End (NEXT) - check termination - Attenuation to Crosstalk Ratio (ACRN) - Check link distance, cable quality/faults, and external interference - **A**ttenuation-**t**o-**c**rosstalk **R**atio, **f**ar **e**nd (ACRF) - check cable quality/faults - Power sum - check cable suitability for gigabit ethernet or higher ## Cable application Issues Make sure a straight thru cable is rated correctly for your application - Crossover cable - terminated with T568A at one end and T568B at the other - connect to a host and another host or hub to hub - auto MDI/MDI-X supported by most modern equipment - Rollover/console cable - Used to connect to serial interface of switches and routers (serial cable) - PoE - Cable must be sufficient quality ## Fiber Optic Cable Testing Tools - Test cable length using optical power meter - Identify locations using **o**ptical **t**ime **d**omain **r**eflectometer (OTDR) - Dirty optical cables - ensure clean environment when splicing/terminating - Incorrect transceivers - Match transceiver wavelength and type at both ends