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 is used to send the broadcast message.
If a server responds, the sensor can show 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 (in msec)
- Lease time reported by the server (in days)
- You can only create this sensor on a probe device (either a local probe, a remote probe, or a cluster probe).
- 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 2 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 IPs is set to Local Probe only. For more information, see section System Administration—Core & Probes.
- Knowledge Base: How can I monitor a DHCP server in a specific network if there are several DHCP networks?
You cannot add this sensor to the Hosted Probe of a PRTG hosted by Paessler instance. If you want to use this sensor, add it to a remote probe device.
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 do not see all setting fields in this dialog. You can change (nearly) all settings in the sensor's Settings tab later.
Select the network interfaces that you want to monitor. PRTG creates one sensor for each interface that you select in the Add Sensor dialog. The settings you select are valid for all sensors that you create when you finish this dialog.
The following settings in the Add Sensor dialog differ in comparison to the sensor's Settings tab.
DHCP Specific |
|
---|---|
Network Interfaces |
Select the network adapters that you want to add a sensor for. You see a list with the names of all items that you can monitor. Add check marks in front of the respective lines to select the desired items. You can also use the check box in the table header to select all items or cancel the selection.
|
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 on which you created the sensor. See the Device Settings for details. For some sensors, you can explicitly define the monitoring target in the sensor settings. See below for details on available settings.
Basic Sensor Settings |
|
---|---|
Sensor Name |
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. |
Parent Tags |
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. |
Tags |
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. There are default tags that are automatically predefined in a sensor's settings when you add a sensor. See section Default Tags below. 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.
|
Priority |
Select a priority for the sensor. This setting determines where the sensor is placed in sensor lists. A sensor with a top priority is at the top of a list. Choose from one star (low priority) to five stars (top priority). |
dhcpsensor
DHCP Specific |
|
---|---|
MAC |
Shows the MAC address of the network adapter that is used to send the broadcast message to the network. Once you have created the sensor, you cannot change this value. It is shown for reference purposes only. If you need to change this value, add the sensor anew. |
Client IP |
Specify if you want to check the returned client IP with a regular expression (regex):
|
Client IP Must Include |
This field is only visible if you enable Check above. In the response of the DHCP server, search by using a regex. If the answer for the client IP does not contain the defined string, the sensor shows a Down status.
|
Client IP Must Not Include |
This field is only visible if you enable Check above. In the response of the DHCP server, search by using a regex. 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.
|
Server IP |
Specify if you want to check the returned server IP with a regex:
|
Server IP Must Include |
This field is only visible if you enable Check above. In the response of the DHCP server, search by using a regex. If the answer for the server IP does not contain the defined string, the sensor shows a Down status. See the example above. Leave empty to not use this field.
|
Server IP Must Not Include |
This field is only visible if you enable Check above. In the response of the DHCP server, search by using a regex. If the answer for the server IP contains the defined string, the sensor shows a Down status. See the example above. Leave empty to not use this field.
|
Timeout (Sec.) |
Enter a timeout in seconds for the request. If the reply takes longer than this value, the sensor cancels the request and shows a corresponding error message. Enter an integer value. The maximum value is 900 seconds (15 minutes). |
DHCP Server Change |
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. Specify how PRTG handles DHCP server changes:
|
Offered IP 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:
|
Sensor Display |
|
---|---|
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.
|
Graph Type |
Define how different channels are shown for this sensor:
|
Stack Unit |
This field 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. |
By default, all of the following settings are inherited from objects that are 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. For more information, see section Inheritance of Settings. To change a setting for this object only, disable inheritance by clicking the button next to inherit from under the corresponding setting name. You then see the options described below.
Scanning Interval |
|
---|---|
Click |
|
Scanning Interval |
Select a scanning interval (seconds, minutes, or hours). The scanning interval determines the amount of time that the sensor waits between two scans. You can change the available intervals in the system administration on PRTG on premises installations. |
If a Sensor Query Fails |
Define the number of scanning intervals that the sensor has time to reach and check a device again in case a sensor query fails. Depending on the option that you select, the sensor can try to reach and check a device again several times before the sensor shows a Down status. This can avoid false alarms if the monitored device only has temporary issues. For previous scanning intervals with failed requests, the sensor shows a Warning status. Choose from:
|
Schedules, Dependencies, and Maintenance Window |
|
---|---|
|
|
Schedule |
Select a schedule from the list. Schedules can be used to monitor for a certain time span (days or hours) every week.
|
Maintenance Window |
Specify if you want to set up a one-time maintenance window. During a maintenance window, the current object and all child objects are not monitored. They are in a Paused status instead. Choose between:
|
Maintenance Begins |
This field is only visible if you enable Set up a one-time maintenance window above. Use the date time picker to enter the start date and time of the maintenance window. |
Maintenance Ends |
This field is only visible if you enable Set up a one-time maintenance window above. Use the date time picker to enter the end date and time of the maintenance window. |
Dependency Type |
Define a dependency type. You can use dependencies to pause monitoring for an object depending on the status of another object. You can choose from:
|
Dependency |
This field is only visible if you enable Select a sensor above. Click the Search button and use the object selector to select a sensor on which the current object will depend. |
Dependency Delay (Sec.) |
This field is only visible if you enable Select a sensor above. Define a time span in seconds for dependency delay. After the master sensor for this dependency comes back to an Up status, monitoring of the dependent objects is additionally delayed by the defined time span. This can help avoid false alarms, for example, after a server restart, by giving systems more time for all services to start up. Enter an integer value.
|
Access Rights |
|
---|---|
Click |
|
User Group Access |
Define the user groups that have access to the selected object. 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:
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.
|
Knowledge Base: How can I monitor a DHCP server in a specific network if there are several DHCP networks?
To change display settings, spike filtering, and limits, switch to the sensor's Overview tab and click the gear icon of a specific channel. For detailed information, see section Sensor Channel Settings.
Click the Notification Triggers tab to change notification triggers. For detailed information, see section Sensor Notification Triggers Settings.
For more general information about settings, see section Object Settings.
For information about sensor settings, see the following sections: