interface, the system processor is interrupted for the time it takes to copy the packet from the
interface buffer to system memory. The processor looks up the Layer 3 destination address for
the packet in the routing table to determine the exit interface. The packet is rewritten with the
correct header for that interface and is copied to the interface. At this time, an entry is also
placed in the fast-switching cache so that subsequent packets for the destination address can use
the same header. The first packet to a destination is always process-switched.
switching cache that was created when a previous packet to the same destination was processed.
With fast switching, a packet is handled immediately, without scheduling an interrupt of the
system processor.
router's queuing mechanisms. Fast switching deals with incoming frames in processor
interrupt mode and minimizes the number of decisions that must be applied. Fast switching
also precaches routes. As soon as an IP destination is process-switched, its route is cached
and is associated with a specific interface. When an IP destination is precached, it is tied to a
specific path.
switching cache located on interface processors. Autonomous switching provides faster packet
switching by allowing the ciscoBus controller to switch packets independently, without having
to interrupt the system processor.