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.