Flow-based monitoring
As mentioned in the chapter introduction, besides polling technology, such as SNMP, we can also use a push strategy, which allows the device to push network information toward the management station. NetFlow and its closely associated cousins, IPFIX and sFlow, are examples of such information pushed from the direction of the network device toward the management station. We can make the argument that the push method is more sustainable since the network device is inherently in charge of allocating the necessary resources to push the information. If the device CPU is busy, for example, it can choose to skip the flow export process in favor of a more critical task such as routing packets.
A flow, as defined by IETF (https://www.ietf.org/proceedings/39/slides/int/ip1394-background/tsld004.htm), is a sequence of packets moving from an application sending something to the application receiving it. If we refer back to the OSI model, a flow is what constitutes a single...
