The RMON (Remote MONitoring) standard was developed in the early 1990's to standardize network monitoring devices (usually referred to as "probes"). At the time, Ethernet LANs consisted of coax cables that where shared by a number of hosts. Repeaters were used to connect the the cables and extend the network. In this environment, a single RMON probe would see all the traffic on the shared network, providing complete network visibility.
Multi-port switches started to become popular in the mid 1990's and SPAN/mirror ports were added to switches to continue to allow probe-based monitoring. The increasing number of ports per switch and the increasing port speeds has made the use of probes a challenge. The need for embedded instrumentation was becoming clear.
In the late 1990's, Cisco introduced the NetFlow protocol, embedding L3-4 monitoring in routers and in 2001 the sFlow protocol was introduced, embedding L2-7 monitoring in switches. Interest in network visibility has accelerated the adoption of the sFlow standard among switch vendors, further limiting the role of probes.
The chart clearly shows the trend toward embedded monitoring. Google Insight for Search was used to trend the popularity of the search terms sFlow, NetFlow, RMON and Probe compared to overall searches relating to Network Monitoring & Management. The sFlow and NetFlow lines track closely and exceed general interest in Network Monitoring & Management, indicating that they are increasingly important topics. The RMON and Probe lines track closely with each other and show a rapid decline compared to Network Monitoring & Management, indicating declining interest in probes as monitoring shifts from probes to embedded instrumentation.
Current trends toward data center convergence increase the need for visibility and control. Complete network visibility is likely to involve both NetFlow and sFlow. NetFlow provides visibility into routers while sFlow extends visibility into the increasingly important switching layer, including: virtual servers, blade servers and edge switches.
Note: The overall downward trend in all the lines results from the increasing population of Internet users. As more people use the Internet, the proportion of Internet users interested in any one topic is diluted. This is particularly true of technical topics. In the past, the technical barriers to using the Internet skewed the user population and resulted in more searches relating to technical topics. Now that everyone is online, the majority of searches relate to more populist topics.