SNMP is an application-layer protocol that provides a message format for communication between managers and agents. The SNMP system consists of an SNMP manager, an SNMP agent, and a management information base (MIB). The SNMP manager can be part of a network management system (NMS) such as Cisco Prime Infrastructure and the agent and MIB reside on the device. To configure SNMP on the device, you define the relationship between the manager and the agent.
The SNMP agent contains MIB variables whose values the SNMP manager can request or change. A manager can get a value from an agent or store a value into the agent. The agent gathers data from the MIB, which is the repository for information about device parameters and network data. The agent can also respond to a manager's requests to get or set data.
An agent can send unsolicited traps to the manager. Traps are messages alerting the SNMP manager to a condition on the network. Traps can mean improper user authentication, restarts, link status (up or down), MAC address tracking, closing of a TCP connection, loss of connection to a neighbor, or other significant events.
SNMP Version 1 and SNMP Version 2 use community strings to authenticate access to the device. If the community string is correct, the device responds with the requested information. If the community string is incorrect, the device discards the request and does not respond.
SNMP Version 3 allows access to the device through a username and password, and an encryption method to improve security.
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