PRTG Manual: DHCP Sensor

Sensor creation

You can create this sensor only on a probe device.

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.

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 adapter on the probe system that is used to send the broadcast message in the Add Sensor dialog.

Knowledge Base

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

Hosted probe

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.

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.

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 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.

PRTG 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.

PRTG 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.

PRTG 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).

If 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.

Regardless 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.

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

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.

You can set a different primary channel later by clicking 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.
  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 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.

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.