Cisco Platform Support For Cef And Dcef; Cef Benefits - Cisco Catalyst 3850 Configuration Manual

Information About CEF

Cisco Platform Support for CEF and dCEF

Cisco Express Forwarding is enabled by default on most Cisco devices running Cisco software. When
Cisco Express Forwarding is enabled on a device, the route processor (RP) performs the express
forwarding.
To find out if Cisco Express Forwarding is enabled on your device, enter the show ip cef command. If
Cisco Express Forwarding is enabled, you receive output that looks like this:
Device# show ip cef
Prefix
[...]
10.2.61.8/24
[...]
If Cisco Express Forwarding is not enabled on your device, the output for the show ip cef command looks
like this:
Device# show ip cef
%CEF not running
When distributed Cisco Express Forwarding is enabled on your device, the line cards perform the express
forwarding.
If Cisco Express Forwarding is not enabled on your device, use the ip cef command to enable Cisco
Express Forwarding or use the ip cef distributed command to enable distributed Cisco Express
Forwarding.

CEF Benefits

•
•
•
IP Switching Cisco Express Forwarding Configuration Guide, Cisco IOS XE Release 3SE (Catalyst 3850
Switches)
2
Next Hop
192.168.100.1
192.168.101.1
Improved performance—Cisco Express Forwarding is less CPU-intensive than fast-switching route
caching. As a result, more CPU processing power can be dedicated to Layer 3 services such as quality
of service (QoS) and encryption.
Scalability—Cisco Express Forwarding offers full switching capacity at each line card when
distributed Cisco Express Forwarding mode is active. Distributed Cisco Express Forwarding is a
distributed switching mechanism that scales linearly with the number of interface cards and the
bandwidth installed in the device.
Resilience—Cisco Express Forwarding offers an unprecedented level of switching consistency and
stability in large dynamic networks. In dynamic networks, fast-switched cache entries are frequently
invalidated by routing changes. These changes can cause traffic to be process-switched through use of
the routing table, rather than fast-switched through use of the route cache. Because the forwarding
information base (FIB) lookup table contains all known routes that exist in the routing table, it
eliminates the need for route cache maintenance and the steps involved with fast-switch or process-
switch forwarding. Cisco Express Forwarding can switch traffic more efficiently than typical demand
caching schemes.
Cisco Platform Support for CEF and dCEF
Interface
FastEthernet1/0/0
FastEthernet6/1