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3527 - Troubleshoot DHCP issue: unknown network segment in NIOS


Your colleagues have created a new subnet and the associated objects to provide leases to newly installed workstations in the subnet. Clients are somehow unable to obtain leases on this subnet. Please investigate and troubleshoot the root cause(s). The DHCP server should be (

Hint: You may log in to the VM testing-windows and use it to simulate client behavior. When working, the testing-windows device should receive a 172.31.101.x IP address.

Estimate Completion Time

  • 15 to 25 minutes






Grid Manager UI



Course References

  • 3012: DHCP Troubleshooting Methodology

Lab Initiation

Access jump-desktop

Once the lab is deployed, you can access the virtual machines required to complete this lab activity. To initiate the lab, click on the jump-desktop tile and login to the Linux UI:

Username: training

Password: infoblox

Initiate lab

To initiate the lab, double-click the Launch Lab icon on the Desktop.

Launch Lab

Launch Lab

Choose the lab number from the list and click OK.

After clicking OK, you will see a pop-up message with a brief description of the lab task. If the description looks correct, click Yes to continue lab initiation.

Lab initiation will take a couple of minutes to finish.

Once complete, you will see another pop-up message with the login credentials and the URL for the Grid Manager’s User Interface. Note that the credentials may differ from those from prior labs.

Screenshot 2024-05-06 at 3.16.57 PM.png


Task 1: Verifying the symptoms

Use the testing-windows VM to verify the symptoms experienced by the users.

Hint: You may use the command ipconfig to view the current lease. Use ipconfig /release to release the lease, and ipconfig /renew to obtain or renew a new lease. Observe server logs while the client is requesting a lease.

Task 2: Reviewing DHCP Member Configuration

Based on the findings from the first task, investigate the DHCP member configuration in the Grid to locate the misconfiguration.


Task 1 Solution: Verifying the symptoms

Use the VM testing-windows to verify the symptoms experienced by the users.

  1. Switch to the VM testing-windows and launch a Command Prompt window.

  2. The command ipconfig shows the device currently does not have a DHCP lease.

  3. Use the command ipconfig /renew to force the device to request for a new DHCP lease. It will fail with an error message about unable to contact DHCP server. This should have generated logs on the DHCP server.

  4. Switch to the VM jump-desktop to the GM web interface.

  5. Navigate to Administration → Logs → Syslog. In Log Viewer Member, select from the drop-down list.

  6. You can see numerous DHCPDISCOVER messages, each with the detail via unknown network segment.

The message unknown network segment suggests that the server is not configured to serve this subnet, We need to investigate the DHCP server configuration next.

Task 2 Solution: Reviewing DHCP Member Configuration

There are 2 places that we should check in the Grid for DHCP configuration: 1) The DHCP member’s configuration, and 2) The DHCP networks' configuration.

Reviewing Member Configuration

  1. Navigate to Data Management → DHCP → Members, select the member ( From the Toolbar, click View DHCP Configuration → IPv4.

  2. This brings out the member’s DHCP configuration file. We can read this configuration file and confirm that there is no subnet for

Reviewing Network Configuration

  1. Navigate to Data Management → DHCP → Networks.

  2. We can see that there is no network for defined.

The likely conclusion at this point is that someone made a mistake entering the network, and typed in instead. Unfortunately, you cannot edit the network once it has been created. To fix the issue, you will need to create a subnet ( and a range ( for the DHCP service to work.

Why not delete the network? It may seem obvious in the lab that this network was created by mistake. However, it is rarely this obvious or simple. Until we have confirmed with the network team that this indeed is a mistake, we should leave the entry in, to avoid disrupting DHCP services for clients on that subnet.

Adding DHCP Configuration

  1. Navigate to Data Management → DHCP → Networks.

  2. Click + to add a new IPv4 network.

  3. Step through the Add IPv4 Network Wizard to add the network Assign it to the member

  4. Click on the newly added network to open it.

  5. Click + to add a new range.

  6. Step through the Add IPv4 Range Wizard to add the range Assign it to the member

  7. Restart services when prompted.

Testing DHCP Configuration

  1. Switch to the VM testing-windows.

  2. Run the command ipconfig /renew. The client should receive a DHCP lease this time.

  3. You can confirm this by observing server logs next.

Verifying Server Logs

  1. Switch to the VM jump-desktop.

  2. In the GM web interface, navigate to to Administration → Logs → Syslog. In Log Viewer Member, select from the drop-down list. You can verify that we see DISCOVER, OFFER, REQUEST, and ACK messages related to this client (testing-windows).

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