Configuring CEF 626

CEF forwarding process
Configuring CEF
To configure CEF on a 3550 switch, you first have to enable IP routing. Remember that because
this is a multilayer switch, only the layer 2 switching processes are enabled by default, to maintain
the plug-and-play nature of all switches. Use the global command ip routing to enable
ip routing, and use the global command ip cef to enable CEF, as follows:
Terry_3550#
Terry_3550#conf t
Enter configuration commands, one per line. End with CNTL/Z.
Terry_3550(config)#ip routing
Terry_3550(config)#ip cef ?
accounting Enable CEF accounting
load-sharing Load sharing
table Set CEF forwarding table characteristics
traffic-statistics Enable collection of traffic statistics
<cr>
Next, you have to convert the layer 2 interface to layer 3. To do this, use the interface command
no switchport. Enable IP on the interface using the standard command, and then enable
CEF on the interface using the ip route-cache cef interface command, as in this example:
Terry_3550#
Terry_3550#
Terry_3550#conf t
Enter configuration commands, one per line. End with CNTL/Z.
Terry_3550(config)#int fa 0/1
Terry_3550(config-if)#no switchport
Terry_3550(config-if)#ip address 192.168.1.1 255.255.255.0
Terry_3550(config-if)#no shut
Terry_3550(config-if)#ip route-cache cef
Terry_3550(config-if)#^Z

Finally, you can confirm that CEF is running on the interface by using the show ip
interface command:
Terry_3550#show ip int fa 0/1
FastEthernet0/1 is down, line protocol is down
Internet address is 192.168.1.1/24
Broadcast address is 255.255.255.255
[output cut]
IP fast switching is enabled
IP fast switching on the same interface is disabled
IP Flow switching is disabled
IP CEF switching is enabled
IP CEF Fast switching turbo vector
IP multicast fast switching is enabled
[output cut]
Terry_3550#
Any entries in the CEF table will be displayed in the following format, using the show ip
cef command:
Terry_3550#sho ip cef fastEthernet 0/1
Prefix Next Hop Interface