Cisco Express Forwarding
Cisco Express Forwarding (CEF) is an advanced layer 3 switching technology used mainly in large core networks or the Internet to enhance the overall network performance. Although CEF is a Cisco proprietary protocol other vendors of multi-layer switches or high-capacity routers offer a similar functionality where layer-3 switching or routing is done in hardware (in an ASIC) instead of by software and the (central) CPU. Function. CEF is mainly used to increase packet switching speed by reducing the overhead and delays introduced by other routing techniques. CEF consists of two key components: The Forwarding Information  Base (FIB) and adjacencies. The FIB is similar to the routing table generated by multiple routing protocols, maintaining only the next-hop address for a particular IP-route. The adjacency table maintains layer 2 or switching information linked to a particular FIB entry, avoiding the need for an Address Resolution Protocol (ARP) request for each table lookup. There are several types of adjacencies. Some are listed below: In order to take full advantage of CEF, it is recommended to use distributed CEF (dCEF), where there is a FIB table on each of the line cards. This avoids the need for  querying the main processor or routing table in order to get the next-hop information. Instead, fast switching will be performed on the line card itself. CEF currently supports Ethernet, Frame Relay, ATM, PPP, FDDI, tunnels, and Cisco HDLC.