Cisco uses three types of packet-forwarding techniques
this process is now extremely complex and involves looking up every destination in the routing table and finding the exit interface for every packet, has the big process problem.
This solution was created to make the slow performance of process switching faster and more efficient. Fast-switching uses a cache to store the most recently used destinations so that lookups are not required for every packet. By caching the exit interface of the destination device, as well as the layer 2 header, performance was dramatically improved.
Cisco Express Forwarding (CEF):
This is Cisco’s newer creation, and it’s the default packet-forwarding method used on all the latest Cisco routers. CEF makes many different cache tables to help improve performance and is change triggered, not packet triggered.