Scan Options
This topic contains the following sections:
The scan options that are applied when running a network scan using the 'Physical Topology' editor are set in the project's 'Settings' editor. The editor is opened by double-clicking the 'Project' node in the PLANT on the left and activating the 'Settings' tab in the 'Project' editor group in the editors area.
The scan options are configured in the following categories:
- 'SNMP' category - allows to configure the version of the SNMP protocol that is used for the SNMP communication.
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'Scan sources' category - used to configure the scan options that are used to search for the Ethernet devices (hereafter referred to as devices) in the network when scanning it.
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'Scan details' category - allows to set additional scan details that are used, for example, to analyze the connections between the devices or to read out additional information from the network devices when scanning the network.
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'Network load' category - allows to set parameters which are used to adjust and control the network load that is generated when performing any network operations. The configured parameters are applied, for example, when scanning the network or when reading/writing SNMP parameters from/to the devices.
'SNMP' category
PLCnext Engineer supports the SNMP versions v1, v2c (default version) and v3. Depending on the selected SNMP version, the corresponding parameter groups and input fields are enabled.
For SNMP version v1 or v2c, the default read and write community strings can be set. The strings are required to get access to a device via Simple Network Management Protocol (SNMP). The SNMP community string is like a password that allows access to the device. The SNMP community string is sent along with an SNMP request (read or write operation) to the device. The default read community string is 'public'. The default write community string is 'private'.
When using SNMP version v3, you can enter a name for the SNMP user and select the authentication and privacy methods and passwords used for the SNMP communication. For devices supporting SNMP version v3, the authentication and privacy methods have to be set which is implemented on the device.
The SNMP settings defined here are used as default settings for all devices to which an SNMP request is sent.
'Scan sources' category
The 'Scan sources' category enables you to configure the scan options. Based on the configured scan options, PLCnext Engineer runs a single scan or successive scans (in cyclic scan mode) to find all devices connected to your network. All reachable devices that respond and the connections between these devices are shown in the 'Physical Topology' editor with their provided device values such as the IP address, subnet mask, system name, etc.
The 'Scan sources' category offers several parameter groups for the scan options supported by PLCnext Engineer. The scan options are not mutually exclusive. It is possible to enable individual or multiple scan options simultaneously. To enable a scan option, activate the 'Enabled' checkbox in the corresponding parameter group.
The following scan options can be configured:
DCP scan
If the 'Enabled' checkbox is activated, the DCP protocol (Discovery and Configuration Protocol) is used to scan for network devices. When scanning, all devices that support DCP will respond to the DCP request and send the requested information back.
From the 'Network adapter' list box, select the network adapter used for the DCP communication. The selection list contains all network adapters that are available in your PC. Network adapters that are currently not connected to the network are visualized by a red cross attached to the symbol in the selection list.
The selection of the network adapter is mandatory.
Ping scan
If the 'Enabled' checkbox is activated, devices are searched using ping scanning. The ping command checks whether devices with an IP address in the defined IP address ranges are reachable in the network.
| Parameter | Description |
| 'Timeout (ms)' | The ping timeout specifies the time in milliseconds after which PLCnext Engineer considers the device as unreachable, i.e., how long the tool waits until a reply from the device.
Value range: 1 to 5,000 ms |
| IP ranges | The address range table contains the IP address ranges that are used for a ping scan. For the ping scan at least one address range must be defined.To define an IP address range, enter the start and end IP address in the table and activate the address range for the network scan by checking the 'Enabled' checkbox'. A new empty address range row is automatically inserted into the table when an address range is confirmed.To delete a configured address range, right-click the row in the table and select 'Delete' from the context menu or press <Del> for a selected row.
Note
The start IP address must be less than the end IP address. |
To exclude specific IP address ranges within the specified ranges from the scan, use the 'Excluded IP ranges' table as described below. |
| Excluded IP ranges | Here you can exclude specific IP address ranges within the specified 'IP ranges' from the scan. For example, if you have a large IP address range configured, you can block individual ranges of addresses that will not be included in the scan.Entering and deleting values in the table are done in the same way as for the 'IP ranges' table (see above). |
SNMP scan
If the 'Enabled' checkbox is activated, devices are searched using Simple Network Management Protocol (SNMP) scanning. When scanning the network, PLCnext Engineer sends an SNMP Broadcast Get Request message to the network. All devices that support SNMP service and respond to this broadcast will be discovered.
| Parameter | Description |
| 'Timeout (ms)' | Set the timeout value in milliseconds while discovering the network devices using SNMP. The timeout specifies the time how long PLCnext Engineer waits for the response of the network device. If the response takes longer than the set time, the SNMP request is aborted. |
| 'Network adapter' | From the 'Network adapter' list box, select the IP configuration of the network adapter used for the SNMP communication. The selection list contains all IP configurations of the network adapters that are available in your PC. The entries consist of the IP address configured for the network adapter and the name of the network connection as it appears in the Network Connections Control Panel program. Network adapters that are currently not connected to the network are visualized by a red cross attached to the symbol in the selection list.The selection of the network adapter is mandatory. |
VRRP scan
If the 'Enabled' checkbox is activated, the network is scanned for virtual routers by analyzing the VRRP (Virtual Router Redundancy Protocol) configuration of the network devices.
With VRRP, two or more physical routers form a VRRP group. The virtual address of the VRRP group is used for communication in the network. In a VRRP group, one router is the master router. All other routers in the VRRP group are backup routers. The master router handles all routing tasks. If the master router fails, a backup router takes over the master router role.
During the network scan, the VRRP configuration of the network device is checked. If the physical address of the device lies within the IP address range specified in the 'IP ranges' table under the 'Ping scan' group, it is checked whether there is a virtual router. If so, the virtual router is shown in the 'Physical Topology' editor in addition to the physical router. (If only the address of the virtual router lies within the specified IP address range, the device is shown as simple Ethernet device.)
Further Info
For details how to enable VRRP for a network device and how to configure the VRRP settings, see the device manual. |
SCB WLAN client scan
If the 'Enabled' checkbox is activated, the network is scanned for WLAN clients that are operated in SCB (Single Client Bridge) mode via SNMP.
In SCB mode, only one Ethernet device may be connected to the WLAN client. The WLAN client adopts the IP address from the Ethernet device behind the client. This means when scanning the network, the Ethernet device will be discovered but not the WLAN client. To find the WLAN client that has the same IP address as the Ethernet device behind the client, configure the 'SCB port' of the WLAN client to which the Ethernet device is connected. In this case, PLCnext Engineer tries to reach the discovered Ethernet device via the selected port. If the Ethernet device is reachable via the port, a second device with the same IP address (in this case the WLAN client) will be shown in the 'Physical Topology' editor.
Discover additional neighbors with LLDP
If the 'Enabled' checkbox is activated, the network is scanned for neighboring devices (devices directly connected to a device) by analyzing the LLDP (Link Layer Discovery Protocol) information of the discovered network device via SNMP.
LLDP is a neighbor-discovery protocol that allows a network device to advertise information about itself to neighboring devices on the local network (LAN). Each network device for which LLDP is enabled sends and receives LLDP messages. The LLDP information is stored in the Management Information Base (MIB) of the network device.
The LLDP setting has no influence on whether the network connections are also examined with the LLDP protocol.
'Scan details' category
The 'Scan details' category provides several parameter groups with additional scan options. These options are used, for example, to analyze the connections between the devices or to read out additional information from the network devices when scanning it with the configured 'Scan Sources' (see above).
The scan options are not mutually exclusive. It is possible to enable individual or multiple scan parameters simultaneously. To enable a scan option, activate the 'Enabled' checkbox in the corresponding parameter group.
The following scan options can be configured:
Detect connections by bridge information
If the 'Enabled' checkbox is activated, connections between devices are detected by analyzing the learned Media Access Control (MAC) addresses stored in the MAC table of the bridge. With deactivated checkbox, only LLDP (Link Layer Discovery Protocol) is used to discover the direct connections between the devices. You should activate the checkbox, if not all devices in the network have LLDP activated. (If all devices in a network have LLDP activated, the scan process can be accelerated by deactivating the checkbox.)
Background: Bridges use the MAC addresses to forward data frames to the destination device. When the data frame arrives at the bridge, the bridge checks whether the destination MAC address is located in its MAC table. If so, then the bridge only sends the frame out of the port that is connected to the destination device. If the destination device is not listed in the MAC table, then the bridge sends the frame out of all ports except the port on which the frame was received. If a device responds to the frame, the bridge learns the MAC address of the sending device in its MAC table.
With activated 'Repeat reading bridge information' checkbox, the MAC address table of the bridges are read multiple times during the network scan. The checkbox should be activated, if the network contains devices which do not provide the MAC table entirely.
Detect ambiguous connections
If the 'Enabled' checkbox is activated, all connections of a network device are analyzed when scanning the network. This also includes ambiguous connections. Ambiguous means, PLCnext Engineer could not detect to which port the connection is routed. With deactivated 'Enabled' checkbox, all connections which could not be uniquely identified, are not shown in the physical topology.
Cyclic scan
The settings made in this category refer to the cyclic scan mode which is turned on/off through the 
button on the toolbar.
In the 'Interval' field, you can set the time interval in [s] between two successive scan operations (default value: 300 s). This means the scan operation is executed repeatedly with the specified interval when the cyclic scan mode is turned on.
With activated 'Enable logging' checkbox, information about changes in the physical topology detected by the scan operations are logged in the MESSAGES window.
'Network load' category
The 'Network load' category provides parameters which are used to adjust and control the network load that is generated when performing any network operations. Here you can, for example, control the intensity of polling that is applied to a single network device or all devices in the network.
The following parameters can be configured:
General
The 'Maximum concurrent requests' parameter defines the maximum number of requests that PLCnext Engineer simultaneously sends to the network devices. This includes the ping requests and the SNMP requests. A higher value will deliver faster results but increases the network load.
Value range: 1 to 99 (default value is 20).
SNMP throttling
The 'SNMP throttling' parameters allow you to control the intensity of SNMP polling that is applied to a single network device or all devices in your network. The settings affect the scanning of SNMP parameters and also the reading and writing of SNMP parameters from and to network devices.
The 'Maximum requests per sec.' parameter defines the maximum number of SNMP requests per second that PLCnext Engineer simultaneously sends to a single device or all network devices according to the setting for the 'Throttling type' parameter. Value range: 1 to 100 (default value is 10).
With 'Throttling type' set to 'Device', the SNMP communication to a single device is affected and with 'Global' the SNMP communication to all network devices is affected.