13 Hierarchical Management Separates Management into Distinct Functions That Are Distributed across Multiple Platforms When the management data are processed before being sent to display and storage devices, then the monitoring devices act as local filters, sending only the relevant data (such as deltas on counter values or updates on events). This can substantially reduce the amount of management data in the network, which is especially important if the monitoring is inband. Thus, we can have monitoring devices at strategic locations throughout the network, polling local devices and network devices, collecting and processing the management data, and forwarding some or all of these data to display and storage devices. The numbers and locations of each type of device will depend on the size of the network, the amount of management data expected to be collected (discussed later in this chapter), and where the displays and storage devices are to be located in the network management architecture. An advantage to hierarchical management is that every component can be made redundant, independent of the other components. Thus, it can be tailored to the specific needs of your network. In some networks it may be preferable to have several display devices, in other networks several processing devices or storage devices. Since these components are separate, the numbers of each can be individually determined. A tradeoff in hierarchical management is the cost, complexity, and overhead of having several management components on the network. 318 CHAPTER 7 Network Management Architecture 7.5.3 Scaling Network Management Traffic Some recommendations are presented here to help determine and optimize the capacity requirements of network management traffic. Recommendation 1. For a LAN environment, start with one monitoring device per IP subnet. For each subnet, estimate values for the following traffic variables: • The number of devices and network devices to be polled • An average number of interfaces per device • The number of parameters to be collected • The frequency of polling (polling interval) Combining these variables gives you an estimate of the average data rate for management traffic per subnet. If this rate is greater than approximately 10% of the capacity (line rate) of the LAN, you may want to consider reducing the amount of management traffic generated, by reducing one or more of the above variables. When the estimated average rate is less than 1% of LAN capacity, this indicates that it may be possible to increase one or more of the above variables. For most of the standard LAN technologies (Ethernet, Fast Ethernet, Gigabit Ethernet, Token Ring, FDDI), the management traffic rate should be targeted at 2% to 5% of the LAN capacity. As LAN capacity increases, you will have more available capacity for network management traffic and may choose to increase one or more traffic variables (Figure 7.14).