Explanation/Reference:
Explanation:
The command to enable Cisco Express Forwarding (CEF) on a Cisco switch is ip cef. This enables CEF
support on the entire switch. All interfaces that are configured to use CEF will be able to. The no form of
this command will disable CEF support, including support on interfaces that have CEF configured on them.
Cisco Express Forwarding allows a Layer 3 switch to determine the next-hop destination MAC address of
the first frame in a transmission made of many frames, and then utilizes the much faster switching process
for all the remaining frames. This requires that routing be enabled on the switch, since the route to the
initial frame must be determined.
The output of the show ip interface vlan id command can be used to determine whether IP routing is
enabled. Partial output of the show ip interface vlan id command for two switches is shown below. The first
(Switch A) has IP routing enabled and the second (Switch B) does NOT have IP routing enabled. The
second switch is missing the section about CEF, since CEF cannot be enabled unless IP routing is
enabled.

The command ip cef distributed is used to enable distributed CEF (dCEF), not the CEF mentioned in the
scenario.
The command ip route-cache cef is a valid command to enable CEF on an individual interface, but the
command is only valid in interface configuration mode.
The command ip cef enable is an invalid command due to incorrect syntax.
Objective:
Layer 2 Technologies
Sub-Objective:
Configure and verify switch administration
References:
Cisco > Cisco IOS IP Switching Command Reference > ip cef