The DHCP sensor monitors a Dynamic Host Configuration Protocol (DHCP) server. It sends a broadcast message to the network and waits for a DHCP server to respond.
The sensor shows the address of the server and the offered IP address in the sensor message. You can check the server's response via regular expressions.
DHCP Sensor
For a detailed list and descriptions of the channels that this sensor can show, see section Channel List.
Sensor in Other Languages
Dutch: DHCP
French: DHCP
German: DHCP
Japanese: DHCP
Portuguese: DHCP
Russian: DHCP
Simplified Chinese: DHCP
Spanish: DHCP
Remarks
You can only create this sensor on a probe device, either a local probe device or a remote probe device.
The probe device where you create a DHCP sensor must have a static IP address. It cannot get its IP address from DHCP because this can cause a DHCP failure that results in a severe issue for the probe device so that you risk losing monitoring data.
Your DHCP sensors show a timeout error if no DHCP is available, or if you use more than two DHCP sensors per device.
Adding a DHCP sensor on a link-local address is valid and is not prohibited. However, as this is a local IP address, the sensor does not receive any data and shows a timeout error.
This sensor does not work if Probe Connection IP Addresses is set to Local probe only, 127.0.0.1 (PRTG is not accessible for remote probes). For more information, see section Core & Probes.
You cannot add this sensor to the hosted probe of a PRTG Hosted Monitor instance. If you want to use this sensor, add it to a remote probe device.
Add Sensor
The Add Sensor dialog appears when you manually add a new sensor to a device. It only shows the settings that are required to create the sensor. You can change nearly all settings on the sensor's Settings tab after creation.
The settings that you select in the Add Sensor dialog are valid for all sensors that you create when you finish the dialog.
DHCP Specific
Setting
Description
Network Interface
Select the network interfaces that you want to monitor. PRTG creates one sensor for each network interface that you select.
Choose the network card on the probe system that is used to send the broadcast message.
Enable check boxes in front of the respective lines to select the items. Use the check box in the table header to select all items or to cancel the selection. In large tables, use the search function in the upper-right corner.
Basic Sensor Settings
Click the Settings tab of a sensor to change its settings.
If the name contains angle brackets (<>), PRTG replaces them with braces ({}) for security reasons. For more information, see the Knowledge Base: What security features does PRTG include?
This setting is for your information only. You cannot change it.
Tags
Enter one or more tags. Confirm each tag with the Spacebar key, a comma, or the Enter key. You can use tags to group objects and use tag-filtered views later on. Tags are not case-sensitive. Tags are automatically inherited.
It is not possible to enter tags with a leading plus (+) or minus (-) sign, nor tags with parentheses (()) or angle brackets (<>).
For performance reasons, it can take some minutes until you can filter for new tags that you added.
The sensor has the following default tags that are automatically predefined in the sensor's settings when you add the sensor:
dhcpsensor
Priority
Select a priority for the sensor. This setting determines the position of the sensor in lists. The highest priority is at the top of a list. Choose from the lowest priority () to the highest priority ().
Usually, a sensor connects to the IP Address/DNS Name of the parent device. See the device settings for details. For some sensors, you can explicitly define the monitoring target in the sensor settings.
DHCP Specific
DHCP Specific
Setting
Description
MAC Address
Shows the MAC address of the network adapter that sends the broadcast message to the network.
PRTG shows this value for reference purposes only. If you need to change this value, add the sensor anew.
Client IP Address
Specify if you want to check the returned client IP address with a regular expression (regex):
Do not check the IP address using a regular expression: The IP address only appears in the sensor message without further processing.
Check the IP address using a regular expression: Enter the regex that you want to use below.
Client IP Address Must Include (Down Status if Not Included)
This setting is only visible if you enable Check the IP address using a regular expression above. In the response of the DHCP server, search by using a regex. If the response for the client IP address does not contain this string, the sensor shows the Downstatus.
For example, enter 10\.0\.5\..* to make sure that any answering DHCP server returns any client IP address starting with 10.0.5.. If it does not, the sensor shows the Down status. Leave this field empty if you do not want to use it.
PRTG supports Perl Compatible Regular Expression (PCRE) regex. For more details, see section Regular Expressions.
Client IP Address Must Not Include (Down Status if Included)
This setting is only visible if you enable Check the IP address using a regular expression above. In the response of the DHCP server, search by using a regex. If the response for the client IP address contains this string, the sensor shows the Down status. See the example above. Leave this field empty if you do not want to use it.
PRTG supports Perl Compatible Regular Expression (PCRE) regex. For more details, see section Regular Expressions.
Server IP Address
Specify if you want to check the returned server IP address with a regex:
Do not check the IP address using a regular expression: The IP address only appears in the sensor message without further processing.
Check the IP address using a regular expression: Enter the regex that you want to use below.
Server IP Address Must Include (Down Status if Not Included)
This setting is only visible if you enable Check the IP address using a regular expression above. In the response of the DHCP server, search by using a regex. If the response for the server IP address does not contain this string, the sensor shows the Down status. See the example above. Leave this field empty if you do not want to use it.
PRTG supports Perl Compatible Regular Expression (PCRE) regex. For more details, see section Regular Expressions.
Server IP Address Must Not Include (Down Status if Included)
This setting is only visible if you enable Check the IP address using a regular expression above. In the response of the DHCP server, search by using a regex. If the response for the server IP address contains this string, the sensor shows the Down status. See the example above. Leave this field empty if you do not want to use it.
PRTG supports Perl Compatible Regular Expression (PCRE) regex. For more details, see section Regular Expressions.
Timeout (Sec.)
Enter a timeout in seconds for the request. Enter an integer. The maximum timeout value is 900 seconds (15 minutes).
If the reply takes longer than this value, the sensor cancels the request and shows a corresponding error message.
DHCP Server Change
If there is more than one DHCP server in the network that can respond to the broadcast message, the sensor can receive a response from a different DHCP server compared to the last scan of the sensor. In this case, PRTG can write an entry to the system logs. Specify how PRTG handles DHCP server changes:
Ignore: Do not write a log entry if the DHCP server changes.
Write log entry: Write an entry to the system logs whenever the DHCP server changes between two sensor scans.
Regardless of this setting, entries are always added to the sensor log.
IP Address Change
If the IP address offered by the DHCP server changes between two sensor scans, PRTG can write an entry to the system logs. Specify how PRTG handles IP address changes:
Ignore: Do not write a log entry if the offered IP address changes.
Write log entry: Write an entry to the system logs whenever the DHCP server offers a different IP address compared to the last sensor scan.
Regardless of this setting, entries are always added to the sensor log.
Sensor Display
Sensor Display
Setting
Description
Primary Channel
Select a channel from the list to define it as the primary channel. In the device tree, the last value of the primary channel is always displayed below the sensor's name. The available options depend on what channels are available for this sensor.
You can set a different primary channel later by clicking below a channel gauge on the sensor's Overview tab.
Graph Type
Define how different channels are shown for this sensor:
Show channels independently (default): Show a graph for each channel.
Stack channels on top of each other: Stack channels on top of each other to create a multi-channel graph. This generates a graph that visualizes the different components of your total traffic. You cannot use this option in combination with manual Vertical Axis Scaling (available in the channel settings).
Stack Unit
This setting is only visible if you enable Stack channels on top of each other as Graph Type. Select a unit from the list. All channels with this unit are stacked on top of each other. By default, you cannot exclude single channels from stacking if they use the selected unit. However, there is an advanced procedure to do so.
Inherited Settings
By default, all of these settings are inherited from objects that are higher in the hierarchy. We recommend that you change them centrally in the root group settings if necessary. To change a setting for this object only, click under the corresponding setting name to disable the inheritance and to display its options.
For more information, see section Root Group Settings, section Scanning Interval.
Schedules, Dependencies, and Maintenance Window
You cannot interrupt the inheritance for schedules, dependencies, and maintenance windows. The corresponding settings from the parent objects are always active. However, you can define additional schedules, dependencies, and maintenance windows. They are active at the same time as the parent objects' settings.
Schedules, Dependencies, and Maintenance Window
For more information, see section Root Group Settings, section Schedules, Dependencies, and Maintenance Window.
Access Rights
Access Rights
For more information, see section Root Group Settings, section Access Rights.
Channel List
Which channels the sensor actually shows might depend on the target device, the available components, and the sensor setup.
Channel
Description
Downtime
In the channel table on the Overview tab, this channel never shows any values. PRTG uses this channel in graphs and reports to show the amount of time in which the sensor was in the Down status
Lease Time
The lease time reported by the server
Response Time
The response time
This channel is the primary channel by default.
More
KNOWLEDGE BASE
How can I monitor a DHCP server in a specific network if there are several DHCP networks?