Cisco Express Forwarding (CEF) is advanced, Layer 3 IP switching technology. CEF improves network performance and scalability.EF is less CPU-intensive than fast switching route caching. More CPU processing power can be dedicated to Layer 3 services such as quality of service (QoS) and encryption. CEF also offers full switching capacity at each line card when distributed CEF (dCEF) mode is active. Finally, CEF offers unparalleled switching stability and performance in large networks. In ever changing networks, fast switching cache entries are often wrong due to routing changes. These changes can cause traffic to be process switched using the routing table, rather than fast switched using the route cache. The Forwarding Information Base (FIB) lookup table contains all known routes that exist in the routing table, it eliminates route cache maintenance and the fast switch/process switch forwarding scenario. CEF can switch traffic more efficiently than typical demand caching schemes.

Configuration

When you enable CEF or dCEF globally, all interfaces that support CEF are enabled by default.

MPLS Forwarding

R2(config)# ip cef

* Enables standard CEF operation * Use in global configuration mode.

To disable CEF, use the no form of this command.

Verification

# show ip cef summary

* Display a summary of the FIB * Use in user EXEC or privileged EXEC mode.

R2# show ip cef summary

IP CEF with switching (Table Version 42), flags=0x0 36 routes, 0 reresolve, 0 unresolved (0 old, 0 new), peak 0 4 instant recursive resolutions, 0 used background process 36 leaves, 51 nodes, 58624 bytes, 44 inserts, 8 invalidations 2 load sharing elements, 752 bytes, 2 references universal per-destination load sharing algorithm, id 0FDE3D1C 3(0) CEF resets, 3 revisions of existing leaves Resolution Timer: Exponential (currently 1s, peak 1s) 2 in-place/0 aborted modifications refcounts: 13398 leaf, 13312 node Table epoch: 0 (36 entries at this epoch) Adjacency Table has 2 adjacencies

# show ip cef

* Display entries in the Forwarding Information Base (FIB) * Use in user EXEC or privileged EXEC mode.

NetStepByStep-R2# show ip cef

Troubleshoot

# debug ip cef table

* Record CEF table events related to the forwarding information base (FIB) table * Use in privileged EXEC mode. * To disable debugging output, use the no form of this command.