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Troubleshooting Cheat Sheet (DRAFT) by

This is a draft cheat sheet. It is a work in progress and is not finished yet.

Layer 1

bad connection
 
cable placement
 
distance limita­tions
 
splitting pairs in a cable
 
cross talk
 
transposed Tx/Rx

Cables & Connec­tions

faulty cables or connec­tions
i.e. broken cables or cable drop in electric box
 
wrong category cable
i.e. video across cat 3

Disatance Limita­tions

Copper cabling max run is 100 meters
 
including Cat5, 5e, 6, 6a & 7
 
Fiber multimode max run is 70 meters

EMI & cross talk

cable running over florecent lights
 
cable tray with electrical and network runs

Switched Transmit & Receive

Switch without MDIX wired w/ straight through rather than crossover
 
Fiber module, port cables may be switched
 
red | receive & black | transmit
 

Layer 2

bad module
 
Layer 2 loops
 
miscon­figured port
 
vlan config­uration

Layer 2 Loops

spanning tree protocol failures can cause a broadcast storm

Port Miscon­fig­uration

check for mismatched speeds, duplex settings, or MDIX settings
 
check host, switch and switch port - turn off auto negotiate

vlan config­uration

all traffic must be routed between vlans
 
all devices must be on the same subnet

Layer 3

duplicate ips
 
incorrect default gateway
 
incorrect dns
 
mismatched mtu
Troubl­esh­ooting LAN & WAN issues w/ routing, sub-ne­tting and services i.e. DNS