SNMP server-side: forwarding server item values as SNMP traps

Owned by Wolfgang Granzer
Jul 12, 2022
3 min read

The server-side of the SNMP driver of the Core Server is also able to send SNMP traps. SNMP traps are SNMP messages that are initiated from the server – without a request from the client. SNMP traps are useful to signal alarm notification or other notifications of abnormal behavior. An SNMP trap has an OID that identifies the trap and one or more variables bindings (OIDs and their values) that are included in the trap. In our SNMP driver, mapped data points can be used as variable bindings for traps. This means that if the underlying server item changes it values, the linked SNMP traps is sent to the configured devices.

Our SNMP driver is supporting all three version of SNMP traps i.e. V1, V2 and V3. For V3, the mandatory security functionality is available to.

SNMP Trap Configuration

The used SNMP version for sending traps is specified within the .

Here the version (V1, V2, V3) can be selected. For V1 and V2 the SNMP secret (SNMP community string) must be defined. For V3, a security user has to be defined.

Each SNMP device has some basic SNMP data points available. The values of these data points (sysName, sysDescription, sysContact and sysLocation) can also be set in the .

If SNMP V1 or V2 is used, the SNMP community string must be known by the SNMP client that receives the trap. If SNMP V3 is used, the security user must be specified within the .

The traps themselves are defined within the .

The first and second column specifies the IP endpoint of the SNMP client that shall receive the trap. The Enterprise OID defines the unique OID of the trap. This OID can freely be chosen - you can use a predefined or enter a new one.

The Variables OID specify the mapped data point i.e. the mapped server items that shall trigger a trigger. The variable OIDs are separated by “,”. It is important to note that the OIDs must exist in the . In the example above, the variables 1.3.6.1.4.1.58651.1 and 1.3.6.1.4.1.58651.2.10 are used. This means that there must be a valid mapping for these two OIDs. E.g.

In this example, the variables 1.3.6.1.4.1.58651.1 and 1.3.6.1.4.1.58651.2.10 of the trap 1.3.6.1.4.1.58651.50 are linked to the Server Items NETx\VAR\Numeric\Item001 and NETx\VAR\Numeric\Item002. This means that whenever the value of one of these items is changed, the Core Server generates a trap with Enterprise OID 1.3.6.1.4.1.58651.50, that includes the variables 1.3.6.1.4.1.58651.1 (with value of NETx\VAR\Numeric\Item001) and 1.3.6.1.4.1.58651.2.10 (with value of NETx\VAR\Numeric\Item002).

If the SNMP server is configured as V1, the so called Generic code and Specific code that is included in the SNMP V1 trap message can be specified too.