Overview of SNMP operations

SNMP manager

The following figure illustrates the SNMP environment.

The SNMP manager, which is installed in the network management station, collects and manages information from the SNMP agents in the managed devices on the network, including the VSP One Block storage systems. The VSP One Block storage systems support SNMP versions v1, v2c, and v3. An RFC-compliant encryption algorithm is adopted for User-based Security Model (USM) authentication.

The devices monitored by the SNMP manager are referred to as managed nodes. Typically, the SNMP manager polls the SNMP agents on a periodic basis. The SNMP manager receives reports from the agents and determines whether the devices are operating normally. If an abnormal event occurs, the SNMP agent can report the condition without a request from the SNMP manager by using a trap message.

When an SNMP manager polls an agent, the following dialogue takes place:

• The SNMP manager sends a request packet to the SNMP agent requesting data regarding the status of the managed node.
• The SNMP agent sends a response packet back to the SNMP manager.
• SNMP uses the TCP/IP User Datagram Protocol (UDP). If the SNMP agent does not respond within a specified time period, the SNMP manager re-sends the request packet. That time period is set by the system administrator, taking into account the network traffic and operation policy.
• If an SNMP agent again does not respond to the resent packet, the SNMP manager assumes that an error has occurred. Depending on the times set for polling and response, this dialogue can take several seconds.

If an SNMP agent detects an abnormal event, it sends a trap to the SNMP manager. However, if a trap is dropped in transmission, the SNMP manager does not know that it was sent. For this reason, you should use both polling and traps to determine whether an abnormal event has occurred.

Message Information Base (MIB)

The standardized configuration and database of network management information is called a Management Information Base (MIB). A standard MIB is common to all SNMP interfaces. An extension MIB is defined by the particular managed device or protocol.

The MIB definition file, VSPStorageSystemMIB.txt, is located in the program\SNMP folder of the software media kit.

SNMP agent

The SNMP Agent for VSP One Block runs on the storage system and communicates with the SNMP manager through the LAN between the storage system and the SNMP manager.

The SNMP agent is implemented on the devices (disk unit, etc.) subject to network management. The SNMP agent collects error information and usage information of the devices and sends it to the SNMP manager.

In the storage system, an SNMP agent is implemented on each AMC. Traps are sent from AMC-0 or AMC-1. In the event of an AMC failure, traps are sent from the healthy AMC. If you are using the SNMP v3 protocol, you must register the SNMP engine ID of each AMC in the SNMP manager.

The following figure shows an example of SNMP operations using an SNMP manager.

The SNMP Agent reports storage system error conditions to the SNMP manager using the SNMP trap function.

The following table lists the types of events that trigger an SNMP Agent trap.

Operations that an SNMP agent can perform fall into the categories GET REQUEST, GETNEXT REQUEST, GETBULK REQUEST, and TRAP. The following table describes the types of SNMP agent operations.

Several different types of errors can be reported when GET REQUEST, GETNEXT REQUEST, and GETBULK REQUEST operations are sent to an SNMP agent. The following table describes the errors that can be reported and suggests corrective action.

You can obtain the status information of certain storage system components from the SNMP Manager. The following table lists the status of storage system components as well as the SNMP trap report functions.