642-812 Building Converged Cisco Multilayer Switched Networks Training Course

Demo Question 7.

Answer: E

Explanation: Cisco Express Forwarding (CEF. is a multilayer-switching technology that allows for increased scalability and performance to meet the requirements of large enterprise networks. CEF has evolved to accommodate the traffic patterns realized by modern networks. These networks are characterized by an increasing number of short-duration flows. Shorter flows are common in environments with a high degree of web-based activity, or other highly interactive types of traffic. CEF uses these strategies to expediently switch data packets to their destinations. It caches information generated by the Layer 3 routing engine. CEF caches routing information in one table (the FIB. and caches Layer 2 next-hop addresses for all FIB entries in an adjacency table. Because CEF maintains multiple tables for forwarding information, parallel paths can exist and enable CEF to load balance per packet. CEF operates in one of two modes. Central CEFmode: The CEF FIB and adjacency tables reside on the route processor, and the route processor performs the express forwarding. Use this CEF mode when line cards are not available for CEF switching, or when features are not compatible with distributed CEF. Distributed Cisco Express Forwarding (dCEF. mode: dCEF is supported on only Cisco Catalyst 6500 switches. When dCEF is enabled, line cards maintain identical copies of the FIB and adjacency tables. The line cards can perform the express forwarding by themselves, relieving the main processor of involvement in the switching operation. dCEF uses an interprocess communications (IPC. mechanism to ensure synchronization of FIBs and adjacency tables on the route processor and line cards. The Cisco term "punt" describes the action of sending a packet "down" to the next-fastest switching level. This list defines the order of preferred Cisco IOS switching methods, from fastest to slowest. 1. Distributed CEF 2. CEF 3. Fast switching 4. Process switching