The All-New Switch Book: The Complete Guide to LAN Switching Technology, Second Edition

17.1. Keeping House

In the early days of internetworking, many bridge and router products implemented the majority of their functionality through software executed on an embedded microprocessor. While this may have been adequate for devices supporting small numbers of ports at relatively low data rates, it is rarely the approach taken today. The time-critical operations in the data path of a modern switch are invariably performed by dedicated hardware.

However, there is still a need for an embedded microprocessor in a hardware-based switch, except in the most basic, cost-driven, unmanaged desktop devices. While all of the fast path functions may be performed by specialized hardware, there are still myriad background processes, support functions, network management, and control protocols that are neither necessary nor practical to implement in dedicated hardware. In general, this housekeeping processor is used for all switch functions that are not in the typical fast path of the data flow.

Figure 17-2 depicts a common configuration for the housekeeping processor subsystem. The system includes a standard microprocessor (CPU) along with memory for storage of both the operational code and frame buffers. The code store is often implemented in nonvolatile memory; EEPROM or Flash ROM is typically used.^[] This allows the housekeeping capability to be available upon device initialization without the need for either code download or a local mass storage device (i.e., disk), while still ...