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Troubleshoot Physical Connectivity Part 3

Updated on December 3, 2014

Troubleshoot Physical Connectivity

Following is one way to troubleshoot this problem:

  1. In the Executive Office, begin troubleshooting the problem by verifying the connectivity problem between the workstation and all other workstations in the network (pinging to all other workstations in the network fails).
  2. In the Executive Office, check the Networking and Sharing Center or the status lights on the NIC. The diagram in the Network and Sharing Center shows the network connection as disconnected from any network, and the link and status lights on the NIC also show it is disconnected. A disconnected status is displayed when the NIC does not have a connection to the network. Possible causes for a disconnected status include:
  • Bad NIC
  • Faulty cable
  • Unplugged cable
  • Switch or hub port either turned off or faulty
In the Executive Office, you should look for common errors or solutions that can be tried quickly. Confirm that the network cable is connected to the NIC and the wall plate. Both ends of the cable are connected correctly. In the Support Office, repeat steps 1 through 3 to duplicate results and discover the scope of the problem. With matching information from each office's workstation, the scope of the problem is shared between these two workstations and likely other workstations. Because the scope of the problem includes two offices, you should look for common errors or solutions that can be tried quickly. In the Networking Closet, check the switch to ensure that it is powered on. The power light for the device indicates it is powered off. Also, since neither the workstation in the Support Office nor the one in the Executive Office could ping in the network, you can conclude that the device is turned off. In the Networking Closet, go to the back of the rack and check the power cable of the switch to ensure that it is plugged into the UPS. The switch is plugged into the UPS, but is not plugged into the critical load section. In the Networking Closet, remove the power cable from a non-critical load (Bank 2) outlet over to an empty critical load (Bank 1) outlet. In the Networking Closet, go to the front of the rack and observe the power light and activity lights for all ports on the switch. The lights are all on and active (except for the wireless access point, as it is still connected to the non-critical load (Bank 2) on the UPS). In the Executive Office or the Support Office, check the Networking and Sharing Center or the status lights on the NIC. The diagram in the Network and Sharing Center shows a connection to the network and Internet, and the lights on the NIC also show it is functioning normally. In the Executive Office or the Support Office, ping each workstation in the network. Each ping attempt now succeeds regardless of the remote workstation.

10.3.12 Troubleshoot Physical Connectivity 4

Following is one way to troubleshoot this problem:

  1. In Office 1, begin troubleshooting the problem by verifying the connectivity problem between the workstation and computer in the Networking Closet (pinging the computer in the Networking Closet fails).
  2. In Office 1, check the Networking and Sharing Center or the status lights on the NIC. The diagram in the Network and Sharing Center shows the network connection as disconnected from any network, and the link and status lights on the NIC also show it is disconnected. A disconnected status is displayed when the NIC does not have a connection to the network. Possible causes for a disconnected status include:
  • Bad NIC
  • Faulty cable
  • Unplugged cable
  • Switch or hub port either turned off or faulty
Because the scope of the problem is currently limited to the Office 1, you should look for common errors or solutions that can be tried quickly. When the user added the speakers, she may have knocked the networking cable loose and disconnected it by accident. Confirm that the network cable is connected to the NIC and the wall plate. The network cable is plugged into the wall plate, but not to the motherboard's NIC. In Office 1, connect the network cable back into the motherboard's NIC, and check the status lights on the NIC. The lights show the connection is functioning normally. In Office 1, check the Networking and Sharing Center diagram and ping the computer in the Networking Closet. The diagram in the Network and Sharing Center shows a connection to the network and Internet, and the ping to the computer in the Networking Closet succeeds.

Explore IP Configuration

In this lab, you should have noted the following:

  1. On Server, the network icon in the System Tray appears normal, which indicates a connection to the local network and to Internet. When you click on the network icon, you see the details of this status.
  2. The Network and Sharing Center diagram confirms that Server is connected to the local network and the Internet.
  3. The ping to Server (local workstation) and the ISP succeed, verifying a valid connection to the Internet.
  4. Using ipconfig /all provides the following information about the Local Area Connection on Server:
  • DHCP Enabled: No. This tells us that the Server is configured with a static IP address and is not enabled for DHCP
  • IPv4 Address: 192.168.0.10
  • Subnet Mask: 255.255.255.0. The Server is using the default subnet mask for the Class C IP address range.
  • Default Gateway: 192.168.0.5

The router's internal interface is configured as the default gateway.

  1. Using tracert 198.28.56.108 verifies a path to the ISP through our default gateway.
  2. In the Executive Office, the link and network activity lights on the back of the workstation are on and blinking, indicating that there is a physical connection to the switch and there is activity on the connection. This points to a TCP/IP configuration problem.
  3. On the Executive Office workstation (Exec), the network icon in the System Tray has a yellow warning sign with an exclamation point which indicates a connection to the local network, but no access to the Internet. When you click on the network icon, you see the details of this status. The Network and Sharing Center diagram confirms that Exec is connected to the local network, but has no Internet access.
  4. On Exec, you are able to ping the local interface on Exec by name (since you don't know the IP address yet), but you can't ping Server or the ISP. This indicates that Exec has a valid connection, but can't communicate with Server or the ISP.
  5. Using ipconfig /all provides the following information about the Local Area Connection on Exec:
  • DHCP Enabled: No
  • IPv4 Address: 192.168.0.62
  • Subnet Mask: 255.255.255.240
  • Default Gateway: 192.168.0.4


This information provides us with at least two clues to the problem:

  1. The network is using DHCP, but this workstation is not enabled for DHCP.
  2. Given the workstation's current subnet mask, the IPv4 Address of the workstation and the Default Gateway are not on the same network. In addition, the subnet mask is not the default subnet mask for the Class C IP address range being used. With 255.255.255.240 as a subnet mask, the network would only include addresses from 192.168.0.48 to 192.168.0.63. The IP address for Server (192.168.0.10) and the ISP fall outside of this range. The information in step 4 confirms that the default subnet mask for the Class C IP address range (255.255.255.0) is being used.
After correcting the subnet mask on Exec, there are still no changes to the network icon or to the diagram in the Network and Sharing Center. After correcting the subnet mask on Exec, you can now ping Server, but you still can't ping the ISP. This indicates that you only have local connectivity. Use tracert 198.28.56.108. The command times out, indicating the following:
  • The ICMP packets are not returning from the first hop (gateway) in its path to the ISP. Exec is not finding the gateway.
  • The gateway address on Exec is not configured correctly. (The gateway address (router) on the network diagram is 192.168.0.5.)
After configuring the correct gateway address on Exec, the network icon and the diagram in the Network and Sharing Center confirm that Exec is connected to the Internet. Using the tracert command again returns a path to the ISP through the gateway. Since we have a valid connection to the Internet, we will leave the static address for now while we troubleshoot in Office 1. In Office 1, the link and network activity lights on the back of the workstation are on and blinking. Once again, this points to a TCP/IP configuration problem. On Office1, the network icon and the diagram in the Network and Sharing Center indicate that Office1 is connected to the Unidentified network and has no Internet access. You are able to ping the local interface, but you can't ping Server or the ISP. This indicates that Office1 has a valid connection to the local network. Using ipconfig /all provides the following information about the Local Area Connection:
  • DHCP Enabled: Yes. This tells us that the workstation is configured to use a DHCP server
  • IPv4 Address: 169.254.201.10. This address is in the APIPA range (169.254.0.1 to 169.254.255.254). This means that the workstation assigned itself an IP address instead of receiving one from the DHCP server. The workstation will only be able to communicate with other hosts on the local network that have also configured their own IP address through APIPA.
  • Subnet Mask: 255.255.0.0. This is the default subnet mask for the APIPA address.
  • Default Gateway: (blank). This means that communication is limited only to other workstations on the local network.
  • DHCP Server line is not shown. This means that the workstation was unable to contact the DHCP server.
  • DNS Servers line is not shown for IPv4.

Since DHCP is enabled, the rest of the information should have come from the DHCP server. We can conclude that there is an issue with the DHCP server.

  1. On Server, launch the DHCP console and activate the scope.
  2. On Office1, the ipconfig /renew command will request new IP address information from the DHCP server, and it will reconfigure the settings for the Local Area Connection.
  3. The ipconfig /all command will check the Local Area Connection configuration. You should notice the line for the default gateway, DNS server, and DHCP server, along with the new IP address which is now within the DHCP scope for the local network.
  4. After activating the DHCP server and receiving a valid IP Address, you can now ping Server from Office1, but you still can't ping the ISP.
  5. The tracert command times out on Office1, indicating that it can't get to the gateway. As noted above the gateway should be 192.168.0.5.
  6. The ipconfig /all command shows the Default Gateway is set to 192.168.0.2, but we know it should be 192.168.0.5. Since this address is coming from DHCP, we need to check the DHCP server.
  7. On Server, launch the DHCP console and reconfigure the settings for the DHCP scope.
  8. On Office1, the ipconfig /renew command will request new IP address information from the DHCP server, and it will reconfigure the settings for the Local Area Connection.
  9. Use the ipconfig /all command to check the Local Area Connection configuration. You should notice the line for the default gateway is now configured correctly.
  10. The network icon and the diagram in the Network and Sharing Center indicate that Office1 is connected to the local network and the Internet.
  11. When you ping the ISP to confirm resolution, the ping succeeds.
  12. On Exec, reconfigure the Local Area Connection to use DHCP.
  13. The ipconfig /all command now shows the IP address, Default Gateway, DNS Server, DHCP Server that were provided by the DHCP server.
  14. The network icon and the diagram in the Network and Sharing Center indicate that Exec is connected to the corporate network with full Internet access.
  15. Use tracert 198.28.56.108, which returns a path to the ISP through the gateway. The network is now fully functional and your troubleshooting is complete.

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