 the packet on the output queue of the appropriate interface. Process Switching 6. The packet is moved from the output queue of the outbound interface to the transmit queue of the outbound interface. Outbound QoS happens in this step. 7. The output interface processor notices the packet in its queue, and transfers the 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. Sec- ond, when the ip_input process finally runs, it references the RIB, which is a very slow process. The ip_input process is run at the same priority level as other pro- cesses 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 performance problems. I've seen 2600 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). A considerable amount of time is also saved becau