Communicating with JMX agents - JMX in Action - page 214

A network management system ( NMS ) sends information to and listens for infor-
mation from agents.
SNMP provides capabilities for the NMS to communicate with the managed
device. The SNMP API has two commands: read and write . The read command is
sent to the agent in order to get information about the current state of a man-
aged device. The write command is used to set the state on the managed device.
Likewise, the managed device can signal the NMS that something interesting has
occurred by sending an SNMP trap . A trap is the SNMP equivalent of a JMX noti-
fication.
Recall from chapter 1 that information about managed devices is stored in a
Management Information Base ( MIB ). The MIB is a hierarchical representation
of information about devices. A managed device can be located on a MIB tree
using an object name or object identifier—for example, organization.dod.enter-
prise.myenterprise.variables.theProduct. An object identifier is a set of numbers
that translates to the textual name. (For more information about MIB s, read the
SNMP specifications at http://www.ietf.org.)
Due to incompatibilities between machines on the Internet, data must be
exchanged using a neutral representation. A standard called Abstract Syntax
Notation One ( ASN . 1 ) was developed to enable this exchange. Using this notation,
people created rules for defining the management information called the Struc-
ture of Management Information (SMI). SMI defines simple types such as integers,
octet strings, and object ids. It also defines application data types such as network
addresses, counters, gauges, time ticks, opaques, integers, and unsigned integers.

9.4.2 Using an SNMP protocol adapter

As with any protocol or transport technology, the flexible JMX architecture
enables agents to communicate with SNMP management applications. An SNMP
adapter translates data from an MBean to an SNMP MIB and uses the SNMP pro-
tocol to transport the information to interested listeners.
Sun Microsystems provides an implementation of an SNMP adapter with a
tool suite included with the JDMK . The toolkit provides the capability to develop
a JMX agent using an SNMP protocol adapter. Using a tool called mibgen, you
can generate MBeans that represent SNMP MIB s. The mibgen tool creates Java
objects for you using your existing MIB definitions. There is even a toolkit to
build an NMS using a management API .
The SNMP protocol adapter can work with SNMP v1 and SNMP v2 protocols.
As the protocol adapter receives requests from the SNMP system, it maps the