<%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. When creating this sensor, choose the network card on the probe system that will be used to send the broadcast message.
If a server responds, the sensor shows the following:
- Address of the server and the offered IP in the sensor message. You can check the server's response using Regular Expressions.
- Response time (msec)
- Lease time given by the server (in days)
DHCP Sensor
Click here to enlarge: http://media.paessler.com/prtg-screenshots/dhcp.png
Remarks
Add Sensor
The Add Sensor dialog appears when you manually add a new sensor to a device. It only shows the setting fields that are required for creating the sensor. Therefore, you will not see all setting fields in this dialog. You can change (nearly) all settings in the sensor's Settings tab later.
Select the desired network interfaces to monitor DHCP servers. PRTG will create one sensor for each network interface you choose in the Add Sensor dialog. The settings you choose will be valid for all sensors that you create when you finish this dialog.
The following settings for this sensor differ in the Add Sensor dialog in comparison to the sensor's settings page.
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Specify Network Interface
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Sensor Settings
On the details page of a sensor, click the Settings tab to change its settings.
Usually, a sensor connects to the IP Address or DNS Name of the parent device where you created this sensor. See the Device Settings for details. For some sensor types, you can define the monitoring target explicitly in the sensor settings. Please see below for details on available settings.
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Sensor Name
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Enter a meaningful name to identify the sensor. By default, PRTG shows this name in the device tree, as well as in alarms, logs, notifications, reports, maps, libraries, and tickets.
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Parent Tags
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Shows Tags that this sensor inherits from its parent device, group, and probe. This setting is shown for your information only and cannot be changed here.
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Tags
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Enter one or more Tags, separated by spaces or commas. You can use tags to group sensors and use tag–filtered views later on. Tags are not case sensitive. We recommend that you use the default value.
You can add additional tags to the sensor if you like. Other tags are automatically inherited from objects further up in the device tree. These are visible above as Parent Tags.
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Priority
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Select a priority for the sensor. This setting determines where the sensor is placed in sensor lists. Top priority is at the top of a list. Choose from one star (low priority) to five stars (top priority).
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MAC
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Shows the MAC address of the network adapter that is used to send the broadcast message to the network. Once a sensor is created, you cannot change this value. It is shown for reference purposes only. If you need to change this, please add the sensor anew.
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Client IP
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Specify if you want to check the returned client IP with a regular expression. Choose between:
- Don't check: The IP will only appear in the sensor message without further processes.
- Check: Enter the regular expression you want to use below.
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Client IP Must Include
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This field is only visible if you choose to Check the client IP above. In the response of the DHCP server, search using a regular expression. If the answer for the client IP does not contain the defined string, the sensor shows a Down status.
For example, enter 10\.0\.5\..* to make sure any answering DHCP server returns an client IP address starting with "10.0.5.". If it does not, the sensor will show an error. Leave empty to not use this field.
For more details, see Regular Expressions section.
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Client IP Must Not Include
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This field is only visible if you choose to check the client IP above. In the response of the DHCP server, search using a regular expression. If the answer for the client IP contains the defined string, the sensor shows a Down status. See the example above. Leave empty to not use this field.
For more details, see Regular Expressions section.
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Server IP
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Specify if you want to check the returned server IP with a regular expression. Choose between:
- Don't check: The IP will only appears in the sensor message without further processes.
- Check: Enter the regular expression you want to use below.
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Server IP Must Include
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This field is only visible if you choose to check the server IP above. In the response of the DHCP server, search using a regular expression. If the answer for the server IP does not contain the defined string, the sensor shows a Down status. See example above. Leave empty to not use this field.
For more details, see Regular Expressions section.
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Server IP Must Not Include
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This field is only visible if you choose to check the server IP above. In the response of the DHCP server, search using a regular expression. If the answer for the server IP contains the defined string, the sensor shows a Down status. Leave empty to not use this field.See example above.
For more details, see Regular Expressions section.
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Timeout (Sec.)
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Enter a timeout in seconds for the request. If the reply takes longer than this value defines, the sensor will cancel the request and show a corresponding error message. Please enter an integer value. The maximum value is 900 seconds (15 minutes).
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DHCP Server Change
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If there is more than one DHCP server in the network that may answer to the broadcast message, the sensor can receive an answer 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. Choose between:
- 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, those entries will always be added to the sensor log.
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Offered IP Change
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If the IP address offered by the DHCP server changes between two sensor scans, PRTG can write an entry to the system logs. Choose between:
- 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, those entries will always be added to the sensor log.
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Primary Channel
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Overview
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Graph Type
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Define how different channels will be shown for this sensor.
- Show channels independently (default): Show an own 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 will generate an easy-to-read graph that visualizes the different components of your total traffic.
This option cannot be used in combination with manual Vertical Axis Scaling (available in the Sensor Channels Settings settings).
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Stack Unit
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This setting is only available if stacked graphs are selected above. Choose a unit from the list. All channels with this unit will be 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.
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Inherited Settings
By default, all following settings are inherited from objects higher in the hierarchy and should be changed there, if necessary. Often, best practice is to change them centrally in the Root group's settings. To change a setting only for this object, disable inheritance by clicking the check mark in front of the corresponding setting name. You will then see the options described below.
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Scanning Interval
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Select a scanning interval (seconds, minutes, or hours) from the list. The scanning interval determines the time the sensor waits between two scans. You can change the available intervals in the system administration on PRTG on premises installations.
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If a Sensor Query Fails
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Define the number of scanning intervals that a sensor has time reach and check a device again in case a sensor query fails. The sensor can try to re-reach and check a device several times, depending on the option you select here, before it will be set to a Down status. This helps you avoid false alarms if the monitored device has only temporary issues. For previous scanning intervals with failed requests, the sensor will show a Warning status. Choose between:
- Set sensor to "down" immediately: The sensor will show an error immediately after the first failed request.
- Set sensor to "warning" for 1 interval, then set to "down" (recommended): After the first failed request, the sensor will show a yellow warning status. If the following request also fails, the sensor will show an error.
- Set sensor to "warning" for 2 intervals, then set to "down": Show an error status only after three continuously failed requests.
- Set sensor to "warning" for 3 intervals, then set to "down": Show an error status only after four continuously failed requests.
- Set sensor to "warning" for 4 intervals, then set to "down": Show an error status only after five continuously failed requests.
- Set sensor to "warning" for 5 intervals, then set to "down": Show an error status only after six continuously failed requests.
Sensors that monitor via Windows Management Instrumentation (WMI) always wait at least one scanning interval until they show an error. It is not possible to set a WMI sensor to "down" immediately, so the first option will not apply to these sensor types. All other options can apply.
If a sensor has defined error limits for channels, it will always show a Down status immediately, so no "wait" option will apply.
If a channel uses lookup values, it will always show a Down status immediately, so no "wait" options will apply.
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Inheritance for schedules, dependencies, and maintenance windows cannot be interrupted. The corresponding settings from the parent objects will always be active. However, you can define additional settings here. They will be active at the same time as the parent objects' settings.
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Schedule
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Select a schedule from the list. Schedules can be used to monitor for a certain time span (days, hours) every week. With the period list option it is also possible to pause monitoring for a specific time span. You can create new schedules and edit existing ones in the account settings.
Schedules are generally inherited. New schedules will be added to existing ones, so all schedules are active at the same time.
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Maintenance Window
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- Not set (monitor continuously): No maintenance window will be set and monitoring will always be active.
- Set up a one-time maintenance window: Pause monitoring within a maintenance window. You can define a time span for a monitoring pause below and change it even for a currently running maintenance window.
To terminate a current maintenance window before the defined end date, change the time entry in Maintenance Ends field to a date in the past.
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Maintenance Begins
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This field is only visible if you enabled the maintenance window above. Use the date time picker to enter the start date and time of the maintenance window.
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Maintenance Ends
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This field is only visible if you enabled the maintenance window above. Use the date time picker to enter the end date and time of the maintenance window.
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Dependency Type
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Define a dependency type. Dependencies can be used to pause monitoring for an object depending on the status of another. You can choose between:
- Use parent: Pause the current sensor if the device, where it is created on, is in Down status, or is paused by another dependency.
- Select object: Pause the current sensor if the device, where it is created on, is in Down status, or is paused by another dependency. Additionally, pause the current sensor if a specific other object in the device tree is in Down status, or is paused by another dependency. Select below.
- Master object for parent: Make this sensor the master object for its parent device. The sensor will influence the behavior of the device, where it is created on: If the sensor is in Down status, the device will be paused. For example, it is a good idea to make a Ping sensor the master object for its parent device to pause monitoring for all other sensors on the device in case the device cannot even be pinged. Additionally, the sensor will be paused if the parent group of its parent device is in Down status, or if it is paused by another dependency.
Testing your dependencies is easy! Simply choose Simulate Error Status from the context menu of an object that other objects depend on. A few seconds later all dependent objects should be paused. You can check all dependencies in your PRTG installation by selecting Devices | Dependencies from the main menu bar.
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Dependency
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This field is only visible if the Select object option is enabled above. Click on the reading-glasses and use the object selector to choose an object on which the current sensor will depend.
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Dependency Delay (Sec.)
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Define a time span in seconds for a dependency delay. After the master object for this dependency goes back to Up status, PRTG will start monitoring the depending objects after this extra delayed. This can help to avoid false alarms, for example, after a server restart, by giving systems more time for all services to start up. Please enter an integer value.
This setting is not available if you choose this sensor to Use parent or to be the Master object for parent. In this case, please define delays in the parent Device Settings or in the superior Group Settings.
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User Group Access
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Define which user group(s) will have access to the object you're editing. A table with user groups and types of access rights is shown: It contains all user groups from your setup. For each user group you can choose from the following access rights:
- Inherited: Use the access rights settings of the parent object.
- None: Users in this group cannot see or edit the object. The object neither shows up in lists nor in the device tree. Exception: If a child object is visible to the user, the object is visible in the device tree, though not accessible.
- Read: Users in this group can see the object and review its monitoring results.
- Write: Users in this group can see the object, review its monitoring results, and edit the object's settings. They cannot edit access rights settings.
- Full: Users in this group can see the object, review its monitoring results, edit the object's settings, and edit access rights settings.
You can create new user groups in the System Administration—User Groups settings. To automatically set all objects further down in the hierarchy to inherit this object's access rights, set a check mark for the Revert children's access rights to inherited option.
For more details on access rights, please see the section User Access Rights.
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More
Knowledge Base: How can I monitor a DHCP server in a specific network if there are several DHCP networks?
Edit Sensor Channels
To change display settings, spike filter, and limits, switch to the sensor's Overview tab and click the gear icon of a specific channel. For detailed information, please see the Sensor Channels Settings section.
Notifications
Click the Notifications tab to change notification triggers. For detailed information, please see the Sensor Notifications Settings section.
Others
For more general information about settings, please see the Object Settings section.
Sensor Settings Overview
For information about sensor settings, please see the following sections: