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Java implementation of SNMP

Developed an Applet, demonstrates functioning of some parts of SNMP protocol using pure java.

A network administrator uses a manager (application program), which is running on NMS (Network Management Station), for interaction with agents (application programs), which are running on the managed nodes.

Each agent maintains its local information database. This database contains variables called in SNMP literature objects. Each object has a unique object identifier. Object identifiers have hierarchical structure and therefore the information database has a tree structure.

The leaves of the tree and the table entries form a set of objects. In the applet, for example, udpLocalPort2 is an object of Agent1 database and sysDescr is an object of Agent2 database.

Each object identifier in the applet implicitly has a prefix "1.3.6.1". A rest part of the identifier you can learn from the database tree according to the labels on the tree nodes.

In addition to the identifier each object has a value and some other properties. You can see the object information at any moment just by clicking on the object.

You as a user of the applet play a role of network administrator.

 

You can open an Option Window by clicking on the Options button and change a transport protocol used with SNMP.

 

You can open a Construct Message Window by clicking on the "Construct Message" Button and construct an SNMP message.

 

You can then send a request message to one of the agents by clicking on the Send button and wait for a response message from it.

 

At any moment you can learn about object properties by clicking on the object.

 

At any moment you can temporarily stop the demonstration process by clicking the Pause button and then resume by clicking the Resume button.


Agent


Implements full SNMP protocol.
Stores and retrieves management data as defined By Management Information   Base.
Can asynchronously signal an event to the manager
Can be a proxy for some non-SNMP manageable network nod.

Manager

Implemented as a Network Management Station
Implements full SNMP Protocol
Able to:
  - Query agents
  - Get responses from agents
  - Set variables in agents
  - Acknowledge asynchronous events from agents

SNMP Protocol

SNMP is based on the manager/agent model. SNMP is referred to as "simple" because the agent requires minimal software. Most of the processing power and the data storage resides on the management system, while a complementary subset of those functions resides in the managed system.

To achieve its goal of being simple, SNMP includes a limited set of management commands and responses. The management system issues Get, GetNext and Set messages to retrieve single or multiple object variables or to establish the value of a single variable. The managed agent sends a Response message to complete the Get, GetNext or Set. The managed agent sends an event notification, called a trap to the management system to identify the occurrence of conditions such as threshold that exceeds a predetermined value. 

In short there are only five primitive operations:

Get (retrieve operation)
Get next (traversal operation)
Get response (indicative operation)
Set (alter operation)
Trap (asynchronous trap operation)

SNMP Message Construct

Each SNMP message has the format:

Version Number
Community Name - kind of a password.
One or more SNMP PDUs - assuming trivial authentication

Each SNMP PDU except trap has the following format:

Request id - request sequence number.
Error status - zero if no error otherwise one of a small set.
Error index - if non zero indicates which of the OIDs in the PDU caused the error.
List of OIDs and values - values are null for get and get next

Trap PDUs have the following format:

Enterprise - identifies the type of object causing the trap
Agent address - IP address of agent which sent the trap
Generic trap id - the common standard traps
Specific trap id - proprietary or enterprise trap
Time stamp - when trap occurred in time ticks
List of OIDs and values - OIDs that may be relevant to send to the NMS

Network Management Architectures

Network management system contains two primary elements: a manager and agents. The Manager is the console through which the network administrator performs network management functions. Agents are the entities that interface to the actual device being managed. Bridges, Hubs, Routers or network servers are examples of managed devices that contain managed objects. These managed objects might be hardware, configuration parameters, performance statistics, and so on, that directly relate to the current operation of the device in question. These objects are arranged in what is known as a virtual information database, called a management information base, also called MIB. SNMP allows managers and agents to communicate for the purpose of accessing these objects.



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