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A network provides ease of communication between computers. To use networks effectively, we need a set of rules by which all the networks should abide. The set of rules is called protocols. Simple Network Management Protocol (SNMP) is one among the various protocols that defines messages related to network management.
In simple terms, SNMP is a primary protocol, used in the transfer of network management information between two or more network entities or nodes.
Let us get to know more about SNMP and its features in the following sections.
Network Management is all about keeping the network up and running, monitoring, and controlling network devices using conventional network technology. Local management and remote management are the two ways of managing a device connected to a network. Local management demands for a human manager where the managed object is situated. When the network devices are more and the network is widespread, management becomes tedious and impossible. Therefore, there arises the need to manage the network remotely. This is enhanced by SNMP.
Using SNMP, one workstation running one or more management software applications can monitor management information collected by thousands of network devices. This information is used to establish the functioning of the network and also to identify the problems in the network.
The ARPANET was the first research network sponsored by the United States Department of Defense (DOD), which connected many universities and government installations using leased telephone lines. When satellite and radio networks were added, trouble brewed and to resolve it, TCP/IP came into existence. This facilitated the connection of multiple networks in a seamless way. On Jan 1 1983, TCP/IP became the only official protocol used by the DOD that marked a decline of the ARPANET. It was then Internet came into existence.
Sometime in the mid-1980s, the growth of Internet was rapid, but there were no standardized network management models. Later, the three models were formulated: the High-Level Entity Management System (HEMS); the Common Management Information Protocol (CMIP) proposed by the Open Systems Interconnection (OSI), a group of International Standards Organization (ISO); and the Simple Gateway Monitoring Protocol (SGMP). CMIP over TCP was formed by the ISO as the actual network management protocol to be used for the Internet. In February 1988, the then Internet Architecture Board (IAB) convened an ad hoc committee to determine which of the three models should be used. It was then decided that CMOT would be a natural choice. The SGMP was the short-term solution before CMOT was distributed.
For an effective transition of systems from SGMP to CMOT, a common network management framework had to be developed that would be used by both the models. This framework was named the Simple Network Management Protocol (SNMP). In April 1989, SNMP was promoted and given a recommended status as the de facto TCP/IP network management framework by the IAB. By then, there were problems between CMOT and SNMP, which led to their independent developments. In May 1990, on reaching a consensus, IAB promoted SNMP as the standard network management protocol and a framework recommended for use on Internet and on all TCP/IP networks.
As the name goes, the protocol is quite simple because it is easy to understand and the agent requires only minimal software. It is this simplicity that serves as a key reason for its widespread acceptance, besides being the chief Internet standard for network management. Implementing SNMP management in a networked device is far more straightforward than most other approaches to network management.
Some of the benefits you derive on using SNMP are as follows.
Standardized protocol: SNMP is the standard network management protocol for TCP/IP networks. Internet Protocols are open, nonproprietary standards developed through voluntary efforts by the Internet community, so is the SNMP that is actively maintained and all future enhancements to SNMP are based on existing protocol standards.
Universal acceptance: All major vendors support SNMP. All SNMP-managed devices use the same type of management interface to support a common set of network management information.
Portability: SNMP is independent of operating system and programming language. The functional design of SNMP is also portable and it defines a core set of operations that must function identically in all devices that support SNMP.
Lightweight: SNMP facilitates the addition of management capability to a device without impacting the operation of the device or its performance. SNMP management may be added to a network device with very little increase in workload and demand on system resources.
Extendibility: SNMP is a core set of operations that remain the same on all managed devices. SNMP has the capability of supporting any type of information on any type of device that may be part of any type of computer network.
Widely deployed: SNMP is one of the most popular protocols in the protocol suite that every vendor is aware of. This popularity serves as one dominant factor for its wide deployment by the vendors.
The three major components of the SNMP that form an integral part of its foundation are the network device, the agent and the manager.
Network device: A network device or the Managed Object is a part of the network that requires some form of monitoring and management.
Agent: An agent is a mediator between the manager and the device. The agent resides inside the network device. It collects the management information from the device and makes it available to the manager. It is to be understood that an agent is a program that resides in the device and is not a separate entity.
A typical agent:
Implements full SNMP protocol.
Stores and retrieves management information as defined in the MIB.
Collects and maintains information about its local environment.
Asynchronously signals an event to the manager .
Acts as a proxy for some non-SNMP manageable network node.
Manager: A manager or management system is a separate entity that manages the agents from a remote place. This is typically a computer that is used to run one or more network management systems. Consider an organization having its branches in different geographical locations. Administration of all the computers present in different localities would be difficult. When the System Administrators computer is installed with the manager and all other systems and devices across all the offices are installed with the agent, management becomes easier. The administrator has to just query the agent through its manger to know the functioning of the device.
A typical manager:
Implements the network management system.
Implements full SNMP protocol.
Queries agents, gets responses from agents, sets variables in agents, and acknowledges asynchronous events from agents.
Communication Between the Manager and Agent: The communication between the manager and the agent in the network is enabled by means of Protocol Data Units (PDUs). These PDUs allow the manager to interact with the agent in the device. The extent of management possible depends on the data available to the manager from the agent.
Before data can be transported across the network, it must be passed down the network mass and encapsulated. PDUs are encapsulated in the User Datagram Protocol (UDP). UDP is a connectionless transport protocol included in the TCP/IP suite and described in RFC 768.
The SNMP network management is composed of three parts to which both the management applications and agents conform. They are:
The protocol, which defines the functioning of the basic operations of SNMP and the format of the messages exchanged by management systems and agents.
Structure of Management Information (SMI), which is a set of rules used to specify the format for defining managed objects or the devices that are accessed using SNMP.
Management Information Base (MIB) is a collection of definitions, which define the properties of the managed object or the device.
The MIB modules and the SMI are expressed using a text-based data description notation called as Abstract Syntax Notation One (ASN.1), which is an unambiguous description of data in an ASCII text format. The MIB data is conveyed across a network using SNMP messages, which are encoded using Basic Encoding Rules (BER). They are similar to SMI, but the messages are encoded in a binary format. Both the ASN.1 and BER are essential for the implementation of SNMP.
SNMP is a request-and-response protocol. The basic SNMP operations performed are categorized as follows.
Retrieving data
Altering variables
Receiving unsolicited messages
Retrieving data: The manager sends a request to an agent to retrieve data by performing the following operations.
GET: The GET operation is a request sent by the manager to the managed object. It is performed to retrieve one or more values from the managed objects.
GETNEXT: This operation is similar to the GET operation. The significant difference is that the GETNEXT operation retrieves the value of the next OID in the tree.
GETBULK: The GETBULK operation is used to retrieve voluminous data from large table.
Altering variables:At times,the manager might want to change the value of a variable.
SET: This operation is used by the managers to modify the value of the network device.
Receiving unsolicited messages: The agent, when faced by problems in the transmission of message, responds to the manager by sending unsolicited messages by using the TRAP operation.
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