Defining the peripheral addresses of the SNMP driver

The SNMP data is provided by external, or internal SNMP agents configured in the chapter configuration panels of SNMP. The data is collected by SNMP managers. The collected data is mapped to DPE values in the WinCC OA database. A SNMP peripheral address has to be configured for the data points that represent the collected data. The peripheral address is configured via an address config, which is added to a data point via the PARA module. Right click on a data point in the PARA module and choose the option insert config. The Insert config panel is opened. Choose the option periphery address and then the option SNMP from the combo box. The SNMP address config is opened:

If the error message Syntax 5" (Datatype conversion incorrect) is shown when using SNMP, add .0 to the end of the related SNMP address.

AgentID: The AgentID corresponds to the number that was used for the configuration of an SNMP agent (when an agent was configured for a manager via the create SNMP agent panel).

OID: The OID is the SNMP object identifier from the MIB file of the agent (in case of WinCC OA the OID of the WinCC OA MIB and otherwise an OID of the MIB file of the agent (of a network device)). In case of a WinCC OA agent a WinCC OA MIB element can be selected using the MIB-Browser (...). Note that you have to add the index number of the data point element from the SNMP Live Agent configuration panel, to the end of the OID chosen via the MIB-Browser. The OID should look e.g. as follows: 1.3.6.1.4.1.13828.2.1.20.1.3.1 (the last number '1' is the data point index from the Live Agent configuration panel).

The peripheral address has the following form: Agentnumber_OID[B]. B is added to the tables when a whole column of the table has to be read. The column (the result) has to be configured on a dyn element. Otherwise the OID has to indicate exactly the desired MIB element. Via the character 'B' you can represent all data point elements of a data point instead of a single element provided via the corresponding index by the Live Agent. All elements of the index 1.3.6.1.4.1.13828.2.1.20.1.2.idx can be represented via 1.3.6.1.4.1.13828.2.1.20.1.2B on a dyn DPE.

To read a list of several OIDs they can be connected using a vertical bar ("|'"), e.g. "1.3.6.1.2.1.2.2.1.10.3|1.3.6.1.2.1.2.2.1.10.7|1.3.6.1.2.1.2.2.1.10.9".

When reading a list of OIDs using the "|" separator, it is not allowed to include a blank!
The List of OIDs is restricted to 4096 characters including the separator.
Trailing dots ".", separators "|" or spaces are removed from the address string
If an address is syntactically incorrect, e.g. if it contains spaces or letters, address mapping stops at this point. No further addresses are mapped, previously mapped addresses are removed from the data point and a message is sent to the Log Viewer.
If one of the addresses polled becomes invalid, the data is marked invalid in the panel. In this case no new values are written, WinCC OA displays the last set of valid data. Since polling continues, the time stamp shown in the panel is not the time stamp of the last valid read but the time stamp of the last poll.
If a request is sent with high number of OIDs it can occur that the corresponding get-request raises a time-out of returns the error that the sent message is "too big". To prevent this, the additional comman ":<n>" (n = number of OIDs per request) can be set to split the request of the array addresses in multiple get-requests, e.g. the address configuration "1.3.6.1.2.1.2.2.1.1.1|1.3.6.1.2.1.2.2.1.1.2|1.3.6.1.2.1.2.2.1.1.3:2" queries 3 OIDs and puts a maximum of 2 OIDs into a single get request.
It is up to the user to decide how many OIDs to query in a single get request. WinCC OA is not able to determine how big an answer to a request might get.

The SNMP driver offers the possibility to browse for data of an agent (OID, value of the Default transformation and data type as text and number). The internal data point element Browse.Start of the type _SNMPV3Entity or _SNMPAgent defines the start-OID from which the browsing should be performed. If no start-OID was defined, the start-OID is automatically "1.3.6.1". The results are written to the specific internal data point element Browse.Result. For further information see Config entries and internal data points.

Subindex: The subindex has a different meaning depending on the send/receive direction. The sending of arrays is not supported in the send direction. Thus, the sub index is in this case always 0. A 64bit number is an exception. For a 64bit number the higher-order part of the number is set via the sub index 1. In the receive direction the sub index 2 always means the OID of the received value (datatype text). This is necessary when a table is read column by column, so that the individual rows can be assigned to an OID. The sub index 1 returns the higher-order part of the number in case of an Uint64. Via the sub index 0 the actual value is accessed. The elements can be polled only when the sub index is 0 (polling = the manager sends a request to the agent and the agent sends a response to the manager).

To use sub index of 2, you also have to use sub index of 0 or else it won't work.

Driver number>: The driver number is the number of the used SNMP manager.

Type of transformation: The data type is specified here. The data type is defined in the MIB file of the agent and has to be specified correctly. The data types are described in the chapter data types and debug levels.

Direction: The direction can be input, output or In/Out. Input means that the data is received by WinCC OA, the output again that WinCC OA provides the data for external SNMP managers. In/Out can be used to be input an output at the same time.

If a get-next-request for some OID returns another OID the value of the DPE is set to null and the invalid bit is set.

Agent version: Here you can specify whether this is a V1/2 agent or a V3 entity.

Note that since a single query (query of an OID) takes more than 100 msecs (100 msec locally. The query via the network can take longer) take care that you do not select a too small interval. If the interval is too small, all OIDs cannot be polled during the specified interval. If an interval of 10 seconds is too short for 130 OIDs, some addresses are only polled every 20 seconds (double interval). Note also that a block query is divided into single queries.

As already mentioned the agents are polled according to the settings of the poll group. The poll group is configured via a separate panel:

The panel allows to create or remove a poll group, specify the poll time and the synchronization time or both. The synchronization time means that the data is synchronized monthly, weekly, daily, every hour or minute. See also chapter poll groups.

MIB-Browser

The MIB-Browser allows to select the OID of a MIB element from a MIB file. It is possible to read non WinCC OA MIB files and browse them hierarchically.

MIBs

ETM MIB

MIB file:

The button allows to select a MIB file and browse the file using the MIB-Browser.

Agent Browsing

Browse / Refresh

The "Browse / Refresh" button allows to get a list of available MIBs from the connected SNMP agent. The MIBs will be stored inside the internal data point of the SNMP agent. See "Load" button below.

Load

The "Load" button allows to load the browsing results from the last "Browse / Refresh" process and browse them using the MIB-Browser.