SNMP protocol

SNMP is a set of Internet Engineering Task Force (IETF) standards for network management, including a protocol, a database structure specification, a set of data objects, and controls for using the protocol. The SNMP protocol is based on the TCP/IP protocol. SNMP has evolved over many years, which has resulted in three major versions of the protocol: SNMPv1, SNMPv2c, and SNMPv3.

Elements of an SNMP model for a managed network are as follows:

Agent: This entity implements the SNMP protocol stack (sometimes called the engine). The agent's role is to receive and respond to requests using the SNMP protocol. It routes requests from managers to the appropriate subagents. It communicates with managers using the SNMP protocol. For z/OS® Communications Server, the agent is the osnmpd daemon.
SubAgents: These entities are sometimes called the monitoring agents. Subagents provide the data that represents the managed objects. They communicate with the agents. An example in z/OS Communications Server is the TCP/IP subagent.
Manager: The role of the manager is to generate requests to retrieve and modify management information. The manager uses the SNMP protocol stack to receive responses from these requests and can also receive notifications, which are unsolicited events. The manager uses the SNMP protocol to communicate with the agent.
Management Information Base (MIB): The MIB defines a set of managed objects. Each managed object has a unique identifier, which is sometimes referred to as an object identifier (OID).
SNMP Messages: Messages are exchanged between the manager and agent entities over the UDP transport of TCP/IP. This facilitates the exchange of SNMP operations. The messages, called PDUs, have formats that are defined by the SNMPv1, SNMPv2c, and SNMPv3 protocols; the types are not interoperable. The messages that are sent and received depend on the role of the entity.