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How can I monitor a DHCP server in a specific network if there are several DHCP networks?



On the probe system with my DHCP sensors are several network adapters. Each adapter is connected to another network with a DHCP server in each network. When I add one DHCP sensor to each available NIC, all sensors only show the network to which the first adapter is connected.

Why does PRTG not send the DHCP request via the NICs to which I add the sensors so that one DHCP sensor gets the response from one specific DHCP server? What can I do to monitor several DHCP networks via several network adapters on one probe system?

dhcp dhcp-sensor nic prtg remote-probe

Created on May 20, 2015 5:13:54 PM by  Gerald Schoch [Paessler Support]

Last change on Jun 10, 2022 8:14:37 AM by  Brandy Greger [Paessler Support]

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Accepted Answer



This article applies as of PRTG 22

Monitoring DHCP servers in different networks

Update: As of PRTG 19.x.50, the behavior of the DHCP sensor changed as follows:

  • It is now possible to monitor multiple DHCP servers in different networks, as the DHCP requests that are sent by the DHCP sensor to monitor a DHCP server are only sent via the previously selected network interface controller (NIC).
  • If no DHCP server is available in the respective network, for example, because the NIC has a link-local IP address, the DHCP sensor times out as expected.

For versions previous to PRTG 19.x.50: Although the DHCP sensor connects to a specific network card, the probe system is responsible for getting a DHCP-based IP address via the DHCP request. For this purpose, the probe system uses any available NIC. Because of this, DHCP sensors only show the DHCP server that sends the first response. The sensors monitor all NICs on which you create them, but they all get the response from the same DHCP server in this case. It is not possible to restrict this sensor type to send the DHCP request to only one specific connected network.

To monitor a specific DHCP network (if you have more than one), add a remote probe to each desired network and create the sensors on the corresponding probe devices. This way, you can monitor each DHCP server individually.

Created on May 20, 2015 5:14:45 PM by  Gerald Schoch [Paessler Support]

Last change on Jan 4, 2023 1:07:38 PM by  Brandy Greger [Paessler Support]

Disclaimer: The information in the Paessler Knowledge Base comes without warranty of any kind. Use at your own risk. Before applying any instructions please exercise proper system administrator housekeeping. You must make sure that a proper backup of all your data is available.