Cisco 3032 Software Configuration Manual page 1019

Chapter 38 Configuring IP Unicast Routing
to be process-switched using the routing table, instead of fast-switched using the route cache. CEF and
dCEF use the Forwarding Information Base (FIB) lookup table for destination-based switching of IP
packets.
The two main components in CEF and dCEF are the distributed FIB and the distributed adjacency tables.
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Because the switch or switch stack uses ASICs to achieve Gigabit-speed line rate IP traffic, CEF or dCEF
forwarding applies only to the software-forwarding path, that is, traffic that is forwarded by the CPU.
The default configuration is CEF or dCEF enabled on all Layer 3 interfaces. Entering the no ip
route-cache cef interface configuration command disables CEF for traffic that is being forwarded by
software. This command does not affect the hardware forwarding path. You can re-enable CEF or dCEF
by using the ip cef or ip cef distributed global configuration command. To enable CEF on an interface
for the software-forwarding path, use the ip route-cache cef interface configuration command.
Caution Although the no ip route-cache cef interface configuration command to disable CEF on an interface is
visible in the CLI, we strongly recommend that you do not disable CEF or dCEF on interfaces except
for debugging purposes.
Beginning in privileged EXEC mode, follow these steps to enable CEF or dCEF globally and on an
interface if it has been disabled:
Command
Step 1
configure terminal
Step 2 ip cef
or
ip cef distributed
Step 3 interface interface-id
Step 4 ip route-cache cef
Step 5
end
Step 6
show ip cef
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The FIB is similar to a routing table or information base and maintains a mirror image of the
forwarding information in the IP routing table. When routing or topology changes occur in the
network, the IP routing table is updated, and those changes are reflected in the FIB. The FIB
maintains next-hop address information based on the information in the IP routing table. Because
the FIB contains all known routes in the routing table, CEF eliminates route cache maintenance, is
more efficient for switching traffic, and is not affected by traffic patterns.
Nodes in the network are said to be adjacent if they can reach each other with a single hop across a
link layer. CEF uses adjacency tables to prepend Layer 2 addressing information. The adjacency
table maintains Layer 2 next-hop addresses for all FIB entries.
Cisco Catalyst Blade Switch 3130 and 3032 for Dell Software Configuration Guide
Purpose
Enter global configuration mode.
Enable CEF operation on a standalone switch,
or
enable dCEF operation on a switch stack.
Enter interface configuration mode, and specify the Layer 3
interface to configure.
Enable CEF on the interface.
Return to privileged EXEC mode.
Display the CEF status on all interfaces.
Configuring Protocol-Independent Features
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