- Network Service Troubleshooting

Question 1

Names not resolving Troubleshooting DNS issues

Answer 1

Troubleshooting DNS issues
• Check your IP configuration
• Is the DNS IP address correct?
• Use nslookup or dig to test - Does resolution work?
• Try a different DNS server - Google is 8.8.8.8 & 8.8.4.4

Question 2

Troubleshooting IP configurations

Answer 2

Troubleshooting IP configurations
• Check your documentation
• IP address, subnet mask, gateway
• Monitor the traffic
• Examine local broadcasts
• Difficult to determine subnet mask
• Check devices around you
• Confirm your subnet mask and gateway
• Traceroute and ping
• The issue might be your infrastructure
• Ping local IP, default gateway, and outside address

Question 3

Troubleshooting duplicate IP addresses

Answer 3

Troubleshooting duplicate IP addresses
• Check your IP addressing - Did you misconfigure?
• Ping an IP address before static addressing
• Does it respond?
• Determine the IP addresses
• Ping the IP address, check your ARP table
• Find the MAC address in your switch MAC table
• Capture the DHCP process
• What DHCP servers are responding?

Question 4

Duplicate MAC addresses

Answer 4

Duplicate MAC addresses
• Not a common occurrence
• MAC addresses are designed to be unique
• May be a man-in-the-middle attempt
• Mistakes can happen
• Locally administered MAC addresses
• Manufacturing error
• Intermittent connectivity
• Confirm with a packet capture, 
should see ARP contention
• Use the ARP command from another computer
• Confirm the MAC matches the IP