PRTG Manual: DHCP Sensor

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.

i_round_blueThe 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

DHCP Sensor

i_square_cyanFor 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.
  • This sensor has a low performance impact.
  • This sensor only supports the IPv4 protocol.
  • See the Knowledge Base: How can I monitor a DHCP server in a specific network if there are several DHCP networks?

i_podYou 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.

i_round_blueThe 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 Interfaces

Select the network interfaces that you want to monitor. PRTG creates one sensor for each network interface that you select.

i_round_blueChoose the network card on the probe system that is used to send the broadcast message.

i_round_blueEnable 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.

Basic Sensor Settings

Basic Sensor Settings

Setting

Description

Sensor Name

Enter a name to identify the sensor.

Parent Tags

Shows tags that the sensor inherits from its parent device, parent group, and parent probe.

i_round_blueThis 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.

i_round_blueIt is not possible to enter tags with a leading plus (+) or minus (-) sign, nor tags with parentheses (()) or angle brackets (<>).

i_round_blueFor 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 (i_priority_1) to the highest priority (i_priority_5).

i_round_blueUsually, 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

DHCP Specific

Setting

Description

MAC Address

Shows the MAC address of the network adapter that sends the broadcast message to the network.

i_round_bluePRTG 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 Down status.

i_speechFor 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.

i_round_bluePRTG 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.

i_round_bluePRTG 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.

i_round_bluePRTG 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.

i_round_bluePRTG 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).

i_round_blueIf 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.

i_round_blueRegardless 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.

i_round_blueRegardless of this setting, entries are always added to the sensor log.

Sensor Display

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.

i_round_blueYou can set a different primary channel later by clicking b_channel_primary 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.
    i_round_redYou 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 b_inherited_enabled under the corresponding setting name to disable the inheritance and to display its options.

i_square_cyanFor more information, see section Inheritance of Settings.

Scanning Interval

Scanning Interval

Scanning Interval

i_square_cyanFor more information, see section Root Group Settings, section Scanning Interval.

Schedules, Dependencies, and Maintenance Window

i_round_blueYou 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

Schedules, Dependencies, and Maintenance Window

i_square_cyanFor more information, see section Root Group Settings, section Schedules, Dependencies, and Maintenance Window.

Access Rights

Access Rights

Access Rights

i_square_cyanFor more information, see section Root Group Settings, section Access Rights.

Channel List

i_round_blueWhich 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 in percent.

Lease Time

The lease time reported by the server

Response Time

The response time in msec

i_round_blueThis channel is the primary channel by default.

More

i_square_blueKnowledge Base

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

What security features does PRTG include?