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ccna on youtube.20.3 SNMP and SPAN Overview20.3.1 Introduction to SNMPSimple Network Management Protocol (SNMP) allows network administrators to manage various nodes on an IP network, such as servers, workstations, routers, switches, and security devices, to help network administrators monitor and manage network performance, find and resolve network faults, and plan for future network growth. The SNMP system consists of 3 parts: NetworkManagementStation (NMS) > SNMP Agent, and Management InformationBase (MIB).1 Network Management Workstation (NMS); a computer running SNMP management software where an administrator can read information from the SNMP agent's MIB or send commands to the SNMP agent for execution.2 Agent: SNMP agent software running on the network device. The NMS can send GetRequest> GetNextRequest and SetRequest requests to the Agent, and the Agent receives the requests from the NMS, performs Read or Write operations according to the packet type, generates a Response and returns it to the NMS. The Agent also proactively sends a trap (Trap) message to the NMS when an abnormal condition or state change occurs in the device (such as a device restart) to report the event that occurred to the NMS..390 . Cisco Networking Lab CCNA Lab Guide (2nd Edition).Management Information Base (MIB): A collection of management objects (Objects) that store data related to device and operational statistics. The MIB organizes variables hierarchically so that management software can monitor and control network devices using MIB variables. The MIB formally defines each variable as an Object ID (OID, ObjectID) O0ID uniquely identifies an object in the MIB hierarchy. The MIB organizes 0IDs into OID hierarchies according to the RFC standard, which are typically displayed as trees. Some common public variables are defined in the RFC, in addition, vendors like Cisco network equipment can define their own tree of dedicated branches to accommodate new variables for vendor devices, belonging to Cisco ODDs as follows: .iso (l).org (3).dod (6).intemet (l).private (4).enterprises (l) .cisco (9), so that the OID is1.3.6.141.9. and the SNMP agent is responsible for providing access to the local MIB.The NMS periodically polls the SNMP agent, but periodic SNMP polling can have a delay with respect to the timing of events and can consume excessive network bandwidth if polling frequency is increased. To compensate for these shortcomings, the SNMP agent can generate and send traps to immediately inform the NMS of certain events o Traps are unsolicited messages that alert the NMS to a condition or event on the network, including important events such as improper user authentication, restarts, link state changes, TCP connection disconnections, OSPF neighbor disconnections, and so on. Traps are directed to notify without sending certain SNMP polling requests, thereby speeding up the response to events and reducing the use of network and agent resources. The SNMP agent opens UDP port 161 to receive requests from the NMS (such as get and set), and the NMS opens UDP port 162 to receive traps sent by the agent.There are three common versions of SNMP in use, and SNMP versions vl, v2c, and v3 are compared as shown in Table 20-3. Among them, the Community string is divided into 2 types, read-only ( RO) and read-write ( RW), and is transmitted in clear text.