That is, the first packet to arrive for a new forwarding is used to build an IP destination cache, which the router refers to in routing subsequent packets to the same network destination. In general, demand caching is a highly efficient method of switching packets. For the most part, demand caching is sufficient and meets the needs of most customer networks. The one significant issue is that of network size and scalability. Because the CEF FIB is simply a mirror of the routing tables, the information is always up to date and provides all possible routing information for a given destination.
Load balancing is a function of knowing all the available paths to a given destination network.
Therefore, if traffic is going to a single destination, we can't do load balancing. It can only be done if there is more than one destination network available across a group of circuits. This feature allows us to do true per-packet load balancing across a number of paths. In general, CEF is feature-independent. Note that if dCEF or any of the other distributed features are used on links above DS3 or E3 speeds, a VIP2-50 card is mandatory.