Introduction to SNMP protocols

Simple Network Management Protocol (Snmp:simple Network Management Protocol). The Simple Network Management Protocol is the SNMP protocol that we often refer to as a set of network management protocols defined by the Internet Engineering Task Force (ietf:internet Engineering task Force). The protocol is based on the Simple Gateway Monitoring Protocol (Sgmp:simple Gateway Monitor Protocol). With SNMP, a management workstation can remotely manage all network devices that support this Protocol, including monitoring network status, modifying network device configuration, receiving network event warnings, and so on.

SNMP is comprised of a series of protocol groups and specifications that provide a way to collect network management information from devices on a network. The management system is established by the management work station, the management node and the Network Management protocol. In the communication process between the management workstation and the managed node, a unified command is used and the command type is very small, making the implementation very simple. Typically, a network management Workstation monitoring node is implemented by reading data on the managed node, while the management workstation can control it by writing data to the managed node. When a particular event is generated by the managed node, the managed node can send a simple network event message to the management workstation, which is called sending a trap and communicating between the management station and the managed node through the Network Management protocol.

The basic principles of SNMP

SNMP uses a special form of the Client/server model: the agent/Management station model. The management and maintenance of the network is done through the interaction between the management workstation and the SNMP agent.      Each SNMP is responsible for answering various queries from the SNMP management station (the primary agent) about MIB definition information. SNMP agents and management stations communicate through standard messages in the SNMP protocol, and each message is a separate datagram. SNMP uses UDP (User Datagram Protocol) as layer Fourth Protocol (transport Protocol) for connectionless operation. The SNMP message packet contains two parts: the SNMP header and the Protocol Data unit PDU. The datagram structure is shown below.

Version Identifier | Public Area | SNMP | Pdu

Version identifier: Ensure that the SNMP agent uses the same protocol, and each SNMP agent discards the datagram that is different from its own protocol version directly.
Common area: For SNMP authentication from agent to SNMP management station; If the network is configured to require authentication, SNMP authenticates the community name and the IP address of the management station from the agent, and if it fails, SNMP sends a failed trap message to the management station from the agent.

Protocol Data Unit (PDU): Where the PDU indicates the SNMP message type and its associated parameters.

Basic services provided by SNMP
5 basic operations are defined in the SNMP V1.0 species. Through these operations, the management system can prepare the management node for effective communication. They are:

1. GET request: Reads a value from a specific variable.
2. GetResponse Request: Intercepts information from a particular variable table.
3. GetNext: Request the value of the next object.
4. Set Request: Used to modify or create an object.
5. The TRAP:SNMP agent sends unsolicited messages to the SNMP management station and is generally used to describe the occurrence of an event.

MIB in SNMP
The Management Information Database (MIB) is an information repository that contains data about configuration and performance in the management agent, an organizational system and a public structure that contains many data objects that are divided into different groups. MIB is the format in which the SNMP agent saves and manages data. The IETF's Management Information base MIB (Management information Base), which defines an accessible network device and its properties, uniquely specified by the object identifier OID (objects Identifier).

The simplicity of SNMP is not only the use of UDP rather than TCP protocol in transmission, but also the complete data structure and control method of SNMP protocol. The approach is to use MIB at both the management station and the node to establish a basic connection. The management workstation has the same MIB information as the managed node.

A MIB is a tree structure in which SNMP protocol messages access devices in the network by traversing nodes in the MIB tree directory. As the following illustration shows, the MIB is a tree-like structure.

ISO (1)
|
ORG (3)
|
DoD (6)
|
Internet (1)
| |
MGMT (2) Private (4)
|
MIB (1)
|
System (1)

The knot on the MIB tree corresponds to an SNMP object whose identification number consists of the number of the root number plus the numbers of the nodes that are routed through the number '. ' Separated. For example, the SNMP object "System" has the following identification number "1.3.6.1.2.1.1". MIB existing two versions, first appear is mib-i (reference RFC1156), after the expansion of Mib-ii (reference RFC1213).