PRTG Manual: DHCP Sensor

Network Interfaces

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.

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.

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 ().

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 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 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.

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.

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

This channel is the primary channel by default.