In the SNMP environment, the server doing collections is known as the Manager. The Manager will directly run a network management station. This is the software package responsible for doing collections and storage.
Some larger designs will distribute polling engines in geographic areas. A polling engine is a piece of software that will issue SNMP requests to manage device’s agents. An agent is a software package that will respond to SNMP requests from managers. In short, the agent runs on the device you wanna monitor.
SNMP can be either read-only or read-write. Read is the ability to only retrieve information. Read-write gives you the ability to change information on a remote device. Writing can be used to adjust informational data, or do things like disable or enable ports on a switch.
Management Information Bases, or MIBs, aren’t always necessary for SNMP’s function, but it makes life much easier. Whenever an SNMP agent is going to be polled, the information is retrieved by asking for specific object identifiers, or OIDs.
OIDs are long strings of numbers in dotted notation. For example, the OID for system description is: 220.127.116.11.18.104.22.168. Think of this like an index. MIBs will take these OIDs, and map them to a hierarchical human-readable form. MIBs generally make it easier to add new monitoring points into an existing monitoring system. Agent requests are received on UDP port 161.
SNMP traps are sent on UDP port 162. Traps are messages that are sent from an agent to a manager when some defined event occurs. When using TLS for encryption, an agent listens on UDP port 10161 and traps are sent on UDP 10162. SNMP Version 1 and Version 2c both implement a simple community-based authentication system. A community is basically just a plain-text password sent to an agent.
In Version 3, there were three main additions: confidentiality by encrypting packets, integrity to ensure packets haven’t been tampered with, and authentication to validate the source. Having a solid NMS is core to administrator sanity. SNMP allows administrators to see trends, predict issues, and react with speed and confidence.
Install and configure SNMP
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