350-401 · Question #613
How does CEF switching differ from process switching on Cisco devices?
The correct answer is D. CEF switching uses proprietary protocol based on IS-IS for MAC address lookup, and process. CEF switching pre-computes and stores forwarding information, including MAC address mappings, for rapid packet forwarding, unlike process switching which performs a full lookup for each packet using the main CPU.
Question
How does CEF switching differ from process switching on Cisco devices?
Exhibit
Options
- ACEF switching saves memory by sorting adjacency tables in dedicate memory on the line cards,
- BCEF switching uses adjacency tables built by the CDP protocol, and process switching uses the
- CCEF switching uses dedicated hardware processors, and process switching uses the main
- DCEF switching uses proprietary protocol based on IS-IS for MAC address lookup, and process
How the community answered
(18 responses)- C6% (1)
- D94% (17)
Why each option
CEF switching pre-computes and stores forwarding information, including MAC address mappings, for rapid packet forwarding, unlike process switching which performs a full lookup for each packet using the main CPU.
CEF generally consumes *more* memory than process switching to build and maintain its FIB and adjacency tables, prioritizing speed over memory savings, and these tables are derived from the routing and ARP tables, not sorted uniquely in dedicated memory to save space.
CDP (Cisco Discovery Protocol) is a discovery protocol and does not build adjacency tables for packet forwarding; adjacency tables are populated from protocols like ARP.
While CEF often leverages dedicated hardware (ASICs) for acceleration, the fundamental distinction from process switching is the *method* of lookup (pre-computed tables vs. per-packet CPU processing), and not all CEF implementations are strictly hardware-based.
CEF (Cisco Express Forwarding) builds a Forwarding Information Base (FIB) and adjacency table to pre-calculate next-hop IP addresses and their corresponding Layer 2 rewrite information (like MAC addresses), enabling very fast MAC address lookups and forwarding decisions, whereas process switching performs these lookups on a packet-by-packet basis using the router's main processor.
Concept tested: Cisco Express Forwarding (CEF) vs. Process Switching
Source: https://www.cisco.com/c/en/us/support/docs/ip/express-forwarding/12015-cef-cef.html
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