Ethernet Issues

LED - status indicators used to diagnose an isse with a connection.

activity, and link speed light .if activity light is off no connection. if it’s solid orange there is a connection. if the light is blinking orange, there is data activity.

a quick look at the ativity light can be a good hint during network troubleshooting.

link speed ling=ght will be off orange or green.

green 1 gbps

orange light 100 mbbps

10 mbps is off..

for most nics this is accurate .

network switches have similare leds for each port.

Duplex mismatch - when one device thinks the connnection is full duplex and tho other thinks it is half duples.

high rate of packet loss wtihout high jitter, high recive erro rrate.

ensure both devices are configured to use auto negotiate.

can manually configure them.

🛠 Copper Cable Issues (Network+)

🔌 Incorrect Pinouts

Most common: mismatch between T568A vs T568B.
Patch panels: usually T568B →
- White/Orange, Orange, White/Green, Blue, White/Blue, Green, White/Brown, Brown.
Wall jacks (keystone): same pinout, 4 pins on each side.
RJ45 connectors: check wiring order by holding connector up to light and counting pins.

⚠️ Bad Port

Symptom: No connectivity, even with a known good cable.
Test with a loopback plug to confirm if the port transmits/receives.
If faulty:
- Replace/switch port on a switch.
- For routers, may need to replace the interface card/module.

🚫 Opens

Definition: No continuity — wire break or no device connected at far end.
Caused by physical damage, loose termination, or cut cable.

🔀 Shorts

Definition: Two wires are improperly touching/connected together.
Often due to poor crimping of RJ45.

🧰 Tools to Identify Issues

Cable Tester → Basic continuity and pinout check.
Cable Certifier → Validates cable meets standards (CAT5e, CAT6, etc.).
Wire Mapper → Checks correct wiring order (pin-to-pin).

⚡ Exam Tip: Know which tool is used for which issue:

Tester = quick check.
Mapper = pinouts.
Certifier = full complianc