Standalone SNMP Agents

The design of the SNMP protocol adaptors 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 standalone 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 needs, as it is impossible to create them through another manager. The advantage of a standalone agent is the reduced size of the application, in terms of memory usage.

This applies to all three versions of SNMP.

Example 18–8 StandAloneSnmpAgent Example

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

public class StandAloneSnmpAgent {

    static SnmpAdaptorServer snmpAdaptor = null;

    public static void main(String args[]) {

        // Parse command line and enable tracing
        [...]

        try {
            // The agent is started on a non standard SNMP port: 8085
            int port = 8085;
            snmpAdaptor = new SnmpAdaptorServer(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 standalone agent uses exactly the same MIB MBeans, with the same customization, as our other agents. However, instead of registering them in the 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. Each of the group MBeans then has two constructors, one with and one without a reference to the MBean server. When table entries are added dynamically, the corresponding object only registers the new entry's MBean if the MBean server reference is non-null; that is, only if the MBean is not instantiated in a standalone agent.

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 standalone agent. If you use a standalone agent for memory considerations, you can remove the registration process from the generated MBean and only customize the init process.

Example 18–9 Customizations in the Generated RFC1213_MIB_Impl.java File

class RFC1213_MIB_IMPL extends RFC1213_MIB {

    public RFC1213_MIB_IMPL() {
	super();
    }
    /**
     * Passing it a name in order to register the same mib in 2 MBeanServer.
     */
    public RFC1213_MIB_IMPL(String name) {
	super();
	mibName = name;
    }
        protected Object createSnmpMBean(String groupName, String groupOid, 
				     ObjectName groupObjname, 
				     MBeanServer server)  {

        // Note that when using standard metadata,
        // the returned object must implement the "InterfacesMBean"
        // interface.
        //
        if (server != null) 
            return new SnmpImpl(this,server);
        else 
            return new SnmpImpl(this);
    }

        protected Object createSystemMBean(String groupName, 
				       String groupOid, 
				       ObjectName groupObjname, 
				       MBeanServer server)  {

        // Note that when using standard metadata,
        // the returned object must implement the "InterfacesMBean"
        // interface.
        //
        if (server != null) 
            return new SystemImpl(this,server);
        else 
            return new SystemImpl(this);
    }

        protected Object createInterfacesMBean(String groupName, 
					   String groupOid, 
					   ObjectName groupObjname, 
					   MBeanServer server)  {

        // Note that when using standard metadata,
        // the returned object must implement the "InterfacesMBean"
        // interface.
        //
        if (server != null) 
            return new InterfacesImpl(this,server);
        else 
            return new InterfacesImpl(this);
    }

}

After the MIB is initialized, it only needs to be bound to the SNMP adaptor, as in the other agents; except that in the standalone case, we use the setSnmpAdaptor method which takes a direct reference to the SNMP adaptor instead of an object name. That is all you need to do when programing a standalone SNMP agent.

You can subclass the MIB and override the group MBean factory method to instantiate your own customized MBean class, replacing for instance new Interfaces() with new InterfacesImpl(), as shown in the code example.

Running the Standalone Agent Example

To Run the Standalone Agent Example

1. Start the standalone agent with the following command:

   $ java -classpath classpath StandAloneSnmpAgent nbTraps

2. If you have not copied the jdmk.acl file to the configuration directory, add the following property to your command line:

   -Djdmk.acl.file=examplesDir/Snmp/Agent/jdmk.acl

   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 the traps. See “Developing an SNMP Manager” for example applications you can use.

   The only limitation of a standalone 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 InetAddressAcl file for access control and traps, unless you have customized the InetAddressAcl mechanism, and you can implement other security schemes as described in Enabling User-Based Access Control.

3. Press Control-C when you have finished running the standalone agent.