Wired Network Troubleshooting (continued)

Question 1

Reversing transmit and receive

Answer 1

Reversing transmit and receive
• Wiring mistake
Easy to find with a wire map
• 1-3, 2-6, 3-1, 6-2
• Simple to identify

Question 2

TX/RX reversal troubleshooting

Answer 2

TX/RX reversal troubleshooting
• No connectivity
• Auto-MDIX might connect
• Try turning it on

Question 3

Damaged cables

Answer 3

• It’s difficult to see inside of the cable

* Check your TDR, replace the cable (if possible)

Question 4

Bottlenecks

Answer 4

Bottlenecks
• There’s never just one performance metric
• A series of technologies working together
• I/O bus, CPU speed, storage access speed,
network throughput, etc.
• One of these can slow all of the others down

Question 5

Interface configuration problems

Answer 5

Interface configuration problems
• Poor throughput
• Very consistent, easily reproducible
• No connectivity
• No link light
• No connectivity
• Link light and activity light

Question 6

Interface configuration

Answer 6

Interface configuration
• Auto vs. Manual configuration
• Personal preference
• Light status
• No light, no connection
• Speed
• Must be identical on both sides
• Duplex
• If mismatched, speed will suffer

Question 7

VLAN mismatch

Answer 7

VLAN mismatch
• Switch is configured with the incorrect VLAN
• Configured per switch interface
• Link light, but no surfing
• A DHCP IP address may not be on the correct subnet
• Manually IP addressing won’t work at all
• Check the switch configuration for VLAN configuration
• Each port should have a VLAN setting
• VLAN 1 is usually the default

Question 8

Duplex/speed match

Answer 8

Duplex/speed match
• Speed and duplex
• Speed: 10 / 100 /1,000 / Auto
• Duplex: Half / Full / Auto
• Incorrect speed
• Many switch configurations will auto-negotiate speed
• Less than expected throughput
• Incorrect duplex
• Again, the switch may auto-negotiate
• Needs to match on both sides
• A mismatch will cause significant slowdowns
• Increase in Late Collisions 
may indicate a duplex mismatch