<%NUMBERING1%>.<%NUMBERING2%>.<%NUMBERING3%> 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_blueThis 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

Consider the following remarks and requirements for this sensor:

Remark

Description

Sensor creation

Static IP address

  • The probe device where you create this 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.

Local probe only

  • 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 the PRTG Manual: Core & Probes.

IPv4

  • This sensor only supports IPv4.

Performance impact

  • This sensor has a low performance impact.

DHCP unavailable

  • This sensor shows a timeout error if no DHCP is available, or if you use more than two DHCP sensors per device.

Link-local address

  • Adding this 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.

Add Sensor dialog

  • Choose the network card on the probe system that is used to send the broadcast message in the Add Sensor dialog.

Knowledge Base

Hosted probe

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.

Basic Sensor Settings

Basic Sensor Settings

Basic Sensor Settings

The sensor has the following default tags that are automatically predefined in the sensor's settings when you add the sensor:

  • dhcpsensor

i_square_cyanFor more information about basic sensor settings, see section Sensor Settings.

DHCP Specific

DHCP Specific

DHCP Specific

Setting

Description

MAC Address

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

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 select 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 information, see section Regular Expressions.

Client IP Address Must Not Include (Down Status if Included)

This setting is only visible if you select 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, this 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 information, 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 select 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, this 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 information, see section Regular Expressions.

Server IP Address Must Not Include (Down Status if Included)

This setting is only visible if you select 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, this 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 information, 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.

If Server Changes

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. Define what PRTG does if DHCP servers change:

  • Ignore (default): Do nothing.
  • 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.

If IP Address Changes

If the IP address offered by the DHCP server changes between two sensor scans, PRTG can write an entry to the system logs. Define what PRTG does if IP addresses change:

  • Ignore (default): Do nothing.
  • 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, PRTG displays the last value of the primary channel 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 this sensor shows different channels:

  • 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 select Stack channels on top of each other above.

Select a unit from the list. PRTG stacks all channels with this unit 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.

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

Lease Time

The lease time reported by the server

Response Time

The response time

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?