packet to the network media. There are a couple of key points in this process that make it particularly slow. First, the processor waits for the next scheduled execution of the ip_input process. Second, when the ip_input process finally runs, it references the RIB, which is a very slow process. The ip_input process runs at the same priority level as other processes on the router, such as routing protocols and the HTTP web server interface. The benefit of process switching is that it is available on every Cisco router platform, regardless of size or age. Packets sourced from or destined to the router itself, such as SNMP traps from the router and Telnet packets destined for the router, are always process-switched. As you can imagine, on large routers or routers that move a lot of packets, process switching can be very taxing. Even on smaller routers, process switching can cause Process Switching Routing Information Base _Input process (RIB) Processor Process memory Input Output Network interface Input/output memory interface Network media media processor processor Figure 15-2. Process switching performance problems. I've seen 2600-series routers serving only a single T1 average 60-80 percent CPU utilization while using process switching. Process switching should never be used as the switching method of choice. Any of the other methods will produce significantly better performance. Interrupt Context Switching Interrupt context switching is much faster than process switching. The increase in speed is largely due to the fact that the ip_input process is rarely called. Interrupt context switching instead interrupts the process currently running on the router to switch the packet. Interrupt context switching usually bypasses the RIB, and works with parallel tables, which are built more efficiently (the details of these tables differ according to the switching path in use). You also save a considerable amount of time because the processor no longer has to wait for a process to complete. The general steps for interrupt c