SNMP - is an Internet standard protocol designed to control various devices in the network based on the architecture of UDP / TCP. These devices include - routers, switches, multiple servers, as well as printers, IP-Telephony, IP-cameras and much more. This protocol is used in network management systems to monitor performance, network-connected devices. SNMP - is a component of TCP / IP and consists of standards intended for network management, which includes: an application layer protocol, database schemas and a set of data objects.

With SNMP, administrators can manage and configure the computers on your network from a central computer, without using a network management program. They can also use SNMP to monitor network performance, identifying network problems and monitoring of those who use the network and how the network is used.

SNMP provides data as variables, which describe the configuration of a control system. These variables are mainly requesting management applications (sometimes they specify).

Control program on the server ("Manager") via SNMP makes the management group of devices in a computer network. On each managed device must be constantly running program ("Agent"), which transmits the information via SNMP «manager." "Manager" processes all the data from the "agents" and converts them into a format suitable for supporting the protocol SNMP. The protocol also solves the problem of control, such as a change and use the new configuration remotely changing derived variables and sending them back "agent." Available via SNMP variables are structured in a specific sequence. These hierarchies, as well as other metadata (for example, the type and variable information) described MIBs or database MIB.

The components of the network management protocols SNMP:
 

•      Controlled device - this equipment or software that can be managed via SNMP and has a one-way (read-only) or bidirectional access to specific information about the item. Managed devices that communicate with the "manager".
•      "Agent" - the software that runs on a managed device. "Agent" for more information on this device and translates this information into a special form for the SNMP protocol, or vice versa (meditation data).
•      Network Management System (NMS) - the software that interacts with the "manager" for supporting overall data structure that reflects the state of the network. It provides the basic operation of data processing required for network management. Any network may be one or more NMS.

Management information base (MIB)

The MIB describes the structure of the managed data using a hierarchical namespace. This space contains the object identifier (OID). Each OID identifies a variable that can be read or set via SNMP.

  Details of the protocol.

SNMP protocol operates at the application layer TCP / IP. "Agent" receives requests on port 161 "Manager" can send it to any available port on the port "agent". "Agent" will respond to the port from which the request will be sent. "Manager" receives notifications (traps) on port 162.

Types of SNMP messages:

GetRequest

This is a request from the "manager" to "agent" to get the value of a variable or list of variables. "Manager" response is returned (response) with the current values​​.

SetRequest

This request from the "manager" to "agent" is used to change a variable or list of variables. Variables themselves are specified in the request body. "Agent" does change in response to the request already specifies the new variable values.

GetNextRequest

This query is used to detect the device available variables and their values. "Manager" response is returned with a value of one variable and the link to the next in the list. The second query retrieves data for the next variable and a reference to another variable. And it passes around.

GetBulkRequest

It is an improved version of GetNextRequest. "Manager" will be returned answer with multiple variables at once, starting with the bound variable in the query.
 

Response

Returns related variables and values ​​of "agent", "manager" for GetRequest, SetRequest, GetNextRequest, GetBulkRequest and InformRequest. Error notification provided fields error status and error index.
 

Trap

Sending messages from an "agent" manager "without prompting" manager. "Includes the current value that identifies the type (trap) and optional related variables. Addressing the recipient is determined using the variables trap-based configurations in the MIB.

InformRequest

It's just a notice from the "manager", "agent", and vice versa. Since SNMP protocol runs on UDP, in which message delivery is not guaranteed, and no indication of lost packets. Help comes InformRequest. He sends a notice of receipt, that is, the recipient is responsible and to answer all of the information is repeated from InformRequest.