In the previous chapter, we used SNMP to query information from network devices. We did this using an SNMP manager to query the SNMP agent residing on the network device with specific tree-structured OID as the way to specify which value we intend to receive. Most of the time, the value we care about is a number, such as CPU load, memory usage, and interface traffic. It's something we can graph against time to give us a sense of how the value has changed over time.
We can typically classify the SNMP approach as a pull method, as if we are constantly asking the device for a particular answer. This particular method adds burden to the device because now it needs to spend a CPU cycle on the control plane to find answers from the subsystem and then accordingly answer the management station. Over time, if we have multiple SNMP pollers querying the same device every 30 seconds (you would be surprised how often this happens), the management overhead...