SNMP sounds simple, right? I mean, it’s right there in the name. So, why does something so simple seem so complex?
To try and keep it at the basics, SNMP is the way a network management system (NMS) speaks with a device, such as a router or switch. The NMS wants to know things about the device, so it queries it for the information it wants.
Imagine a warehouse where a bunch of people pack fruit coming down a conveyor belt into boxes. On the conveyor belt are all sorts of fruits—bananas, limes, coconuts, apples, and more. People are assigned to fill up boxes with one type of fruit, so they pick it off the belt and put it in a box.
There’s a man in the room next door behind a closed door that cannot be opened. He’s supposed to keep track of how much of each type of fruit there is and report it to management. His name is NMS. There’s another man in the room with all the fruit packers whose job is to keep track of how much fruit is in each box. He’s the Agent.
Every so often, NMS will ask the Agent “How many bananas?” or “How many apples?” The Agent will then ask the people packing the boxes how many and relay the answer to NMS through the door.
This is basically how SNMP works. The NMS system queries the agent on the device for whatever value it desires. The agent finds the values from the hardware doing the work and relays it back to the NMS. Instead of fruits in a box, it asks about how many bytes went through an interface, or what the current CPU usage is. But the agent knows how to get these values from the device and how to speak to the NMS.