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Java Dynamic Management Kit 4.0 Tutorial

Stand-Alone SNMP Agents

The design of the SNMP protocol adaptor and of the MBeans generated by mibgen give you the option of creating an SNMP agent that is not a Java Dynamic Management agent.

This stand-alone agent has no MBean server and thus no possibility of being managed other than through the SNMP protocol. The application must instantiate all MIBs that the SNMP agent will need, as it will be impossible to create them through some other manager. The advantage of a stand-alone agent is the reduced size of application, in terms of memory usage.

Example 7-7 The StandAloneSnmpAgent Example

import com.sun.jdmk.Trace;
import com.sun.jdmk.comm.SnmpAdaptorServer;

public class StandAloneSnmpAgent {

    static SnmpAdaptorServer snmpAdaptor = null;

    public static void main(String args[]) {

        // enable tracing
        [...]

        try {
            // The agent is started on a non standard SNMP port: 8085
            int port = 8085;
            snmpAdaptor = new SnmpAdaptorServer(port);
            java.lang.System.out.println(
                "NOTE: SNMP Adaptor is bound on port " + port);

            // Start the adaptor
            snmpAdaptor.start();

            // Send a coldStart SNMP Trap
            snmpAdaptor.sendV1Trap(0, 0, null);

            // Create the MIB you want in the agent (ours is MIB-II subset)
            RFC1213_MIB mib2 = new RFC1213_MIB();

            // Initialize the MIB so it creates the associated MBeans
            mib2.init();

            // Bind the MIB to the SNMP adaptor
            mib2.setSnmpAdaptor(snmpAdaptor);

            // Optional: create a LinkTrapGenerator
            int ifIndex = 1;
            LinkTrapGenerator trapGen = new LinkTrapGenerator(ifIndex);
            trapGen.start();

        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    // Needed to get a reference on the SNMP adaptor object
    static public SnmpAdaptorServer getSnmpAdaptor() {
        return snmpAdaptor;
    }
}

As this example demonstrates, the stand-alone agent uses exactly the same MIB MBeans, with the same customization, as our other agents. However, instead of registering them in MBean server, they are only instantiated. And whereas the registration process creates all subordinate MBeans of the MIB, now we must call its init method explicitly. The init method performs the same function as the preRegister method, only it does not register the MBean with the MBean server.

The mibgen tool automatically generates both the pre-registration methods and the init methods in the MIB MBeans. Therefore, no special action is necessary to use them in either a regular agent or a stand-alone agent. If you use a stand-alone agent for memory considerations, you can remove the registration process from the MBean and only customize the init process.

In our example, we have applied the customizations to both processes so that the MIB can be used by either agent. In the following code, customizations are noted with MODIF_ comments:

Example 7-8 Customizations in the Generated RFC1213_MIB.java File

public class RFC1213_MIB extends SnmpMib implements Serializable {

    // Default constructor. Initialize the Mib tree
    public RFC1213_MIB() {
        mibName = "RFC1213_MIB";
    }

    // Initialization of the MIB with no registration in the MBean server
    public void init() throws IllegalAccessException {
        // Allow only one initialization of the MIB
        if (isInitialized == true) {
            return ;
        }

        // Initialization of the "Snmp" group
        {
            SnmpMeta meta = new SnmpMeta((SnmpMib)this);
// MODIF_BEGIN
            //meta.setInstance(new Snmp((SnmpMib)this));
            meta.setInstance(new SnmpImpl((SnmpMib)this));
// MODIF_END
            root.registerNode("1.3.6.1.2.1.11", (SnmpMibNode)meta);
        }

        // Initialization of the other groups
        [...]

        isInitialized = true;
    }

    // Initialization of the MIB with AUTOMATIC REGISTRATION
    // in the MBean server
    public ObjectName preRegister(MBeanServer server, ObjectName name)
        throws Exception {

        // Allow only one initialization of the MIB
        if (isInitialized == true) {
            throw new InstanceAlreadyExistsException();
        }

        // Initialize MBeanServer information
        this.server = server;

        // Initialization of the "Snmp" group
        {
            SnmpMeta meta = new SnmpMeta((SnmpMib)this);
// MODIF_BEGIN
            //Snmp instance = new Snmp((SnmpMib)this, server);
            Snmp instance = new SnmpImpl((SnmpMib)this, server);
// MODIF_END
            meta.setInstance(instance);
            root.registerNode("1.3.6.1.2.1.11", (SnmpMibNode)meta);
            server.registerMBean(
                instance, new ObjectName(mibName + ":name=Snmp"));
        }

        // Initialization of the other groups
        [...]

        isInitialized = true;
        return name;
    }

    private boolean isInitialized = false;

}

After the MIB is initialized, it only needs to be bound to the SNMP adaptor, as in the other agents. That is all you need to do when programing a stand-alone SNMP agent.

Running the Stand-Alone Agent Example

Launch the stand-alone agent with the following command:


$ java -classpath classpath StandAloneSnmpAgent

You should see the same initialization messages as with the simple agent. Then, you should see the agent sending out a trap every two seconds. If you have an SNMP manager application, you can send requests to the agent and receive its traps. See "Developing an SNMP Manager" for example applications you can use.

The only limitation of a stand-alone agent is that you cannot access or manage the SNMP adaptor and MIB MBeans in the dynamic management sense. However, the SNMP adaptor still relies on the ACL file for access control and traps, and you can implement other security schemes as described in "Message-Level Security".

Type "Control-C" when you are done running the stand-alone agent.