SNMP Protocol Introduction

SNMP: Simple Network Management Protocol ). Simple Network Management Protocol (SNMP) is a set of network management protocols defined by the Internet Engineering Task Force (IETF: Internet Engineering Task Force. This Protocol is based on the simple gateway monitoring protocol (sgmp: simple gateway monitor protocol ). Using SNMP, a management workstation can remotely manage all network devices that support this protocol, including monitoring network status, modifying network device configurations, and receiving network event warnings.

SNMP is composed of a series of protocol groups and specifications. It provides a method to collect Network Management Information from devices on the network. The management system is established by management workstations, managed nodes, and network management protocols. When the management workstation communicates with the managed node, the implementation becomes very simple by using unified commands with few command types. Generally, the network management workstation monitors nodes by reading data from the managed nodes. At the same time, the management workstation can also control it by writing data to the managed nodes. When a managed node generates a special event, the managed node can send a simple network event message to the management workstation. This process is called sending a trap, the management workstation and the managed node communicate through the Network Management Protocol.

Basic Principles of SNMP

SNMP adopts a special form of client/server model: Agent/management station model. Network management and maintenance are completed through the interaction between the management workstation and the SNMP agent. Each SNMP agent is responsible for answering various queries on the MIB definition information of the SNMP management workstation (master agent. The SNMP Agent communicates with the management site through standard messages in the SNMP protocol. Each message is a separate datagram. SNMP uses UDP (User Datagram Protocol) as the layer-4 protocol (Transport Protocol) for connectionless operations. The SNMP message consists of two parts: the SNMP header and the Protocol Data Unit PDU. The datagram structure is shown in.

Version ID | public zone | SNMP | PDU

Version identifier: Make sure that the SNMP agent uses the same protocol. Each SNMP agent directly discards the datagram that is different from its own Protocol version.
Public Zone: used for SNMP Authentication on the SNMP Management site from the proxy. If the network is configured to require verification, the SNMP slave agent authenticates the group name and the IP address of the Management site. If the authentication fails, SNMP sends an authentication failure Trap Message from the agent to the management site.

Protocol Data Unit (PDU): PDU indicates the Message Type and related parameters of SNMP.

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

1. GET request: Read a value from a specific variable.
2. getresponse request: extract information from a specific variable table.
3. getnext: Request the value of the next object.
4. Set Request: used to modify or create objects.
5. Trap: the SNMP agent sends a non-Request Message to the SNMP Management site, which 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. It has an organizational system and a public structure, it contains multiple data objects belonging to different groups. MiB are the storage and management data formats of the SNMP agent. The Management Information Base defined by IETF defines accessible network devices and their attributes, which are uniquely specified by the object identifier oid.

The simplicity of SNMP is not only that UDP is used for transmission, but also that the SNMP protocol has a complete data structure and a control method. The method is to use MIB on both the management workstation and node to establish basic connections. The management workstation and the managed node have the same MIB information.

MiB is a tree structure. SNMP messages access devices in the network by traversing nodes in the MIB Tree directory. As shown in, MIB is a tree structure.

ISO (1)
|
Org (3)
|
DOD (6)
|
Internet (1)
|
MGMT (2) Private (4)
|
MiB (1)
|
System (1)

The pairing on the MIB tree should be an SNMP object. Its identification number is composed of the root number and the ending number through the path. The numbers are separated '.. for example, the SNMP object "system" has the following identification number "1.3.6.1.2.1.1 ". miB has two versions, the first is the MIB-I (refer to rfc1156), and then expanded to the MIB-II (refer to rfc1213 ).