2.7.2 Developing an SNMP Agent

An SNMP agent is an application that responds to SNMP requests formulated as get, set, getnext, and getbulk operations on variables defined in a MIB. This behavior can be fully mapped onto the MBean server and MBean resources of a Java dynamic management agent, provided that those MBeans specifically implement the MIB. An SNMP agent can be issued either with or independently from an MBean server.

There are two SNMP protocol adaptors: one that supports SNMPv1 and v2, and another introduced in the Java DMK 5.0 that supports SNMPv3 as well as the two previous versions. All features added in the Java DMK 5.0 therefore support SNMPv3 USM MIBs, providing user-based security, and scoped MIBs, that can be registered in the adaptor using a context name. The addition of multithread support in SNMP adaptors and timers in Java DMK 5.0 has also improved the performance of SNMP.

The SNMP protocol adaptors respond to requests in SNMP and translate the requests into management operations on the specific MIB MBeans. The SNMP adaptors also send traps, the equivalent of a JMX agent notification, in response to SNMP events or errors.

The SNMP protocol adaptors can manage an unlimited number of different MIBs. These MIBs can be loaded or unloaded dynamically, by registering and unregistering the corresponding MBeans. The adaptors attempt to respond to an SNMP request by accessing all loaded MIBs. However, MIBs are dynamic only through the agent application, and the SNMP protocol does not support requests for loading or unloading MIBs.

One advantage of the dual JMX–SNMP agent is that MIBs can be loaded dynamically in response to network conditions, or even in response to SNMP requests. Other Java dynamic management applications can also access the MIB through its MBean interface. For example, the value of a MIB variable might be computed in another application and written by a call to the MBean setter.

The SNMP protocol adaptors also send inform requests from an SNMP agent to an SNMP manager. The SNMP manager sends an inform response back to the SNMP agent.