SNMPII Driver

The SNMPII driver enables Ethernet-based communication between Plant SCADA and a Simple Network Management Protocol (SNMPII) system.

The maximum request length for the SNMPII protocol is 255 bytes (2040 bits) for a string. Strings use one SNMP request per string tag, while numeric data can be grouped into one SNMP request.

Citect SCADA 7.20 or later (or a later version of Plant SCADA) is required to use the SNMPII Driver.

About SNMPII

SNMPII is a request-and-response protocol. An SNMP manager sends a request to an agent. The agent replies with a response that indicates if the operation was performed successfully or if an error is detected.

Each SNMP operation has its own type of message. Each of these messages is used by a management system to request that an operation be performed on managed variables maintained by an SNMP agent. There are three request and response operations: Get, GetNext, and Set.

A fourth operation, Trap, is an unsolicited message sent by an agent; it therefore does not have a corresponding request message. Trap messages can be generated for changes such as host system startup, shutdown, or password violation. Trap destinations can be configured by a user, but the occurrences which generate a trap message are internally defined by the SNMP agent.

The SNMPII protocol specifies the behavior of the Get, GetNext, Set, and Trap operations, and defines the format of the SNMP messages exchanged by managers and agents.

Note:
• The Plant SCADA driver does not support the GetNext request.

• SNMPII driver supports SNMP GETS and PUTS (read and write), trap receiving, forwarding and trap generation. Each device runs in a separate NT thread for maximum speed.

• If an SNMP device only supports a fixed IP reply address, then Plant SCADA I/O Server redundancy will not be supported for that device.

• SNMPII driver has partial support for SNMP protocol version V2C and currently it supports only the SNMP GETS and PUTS (read and write) operation. The other operations will be supported in the future release version of this driver.