Cisco Express Forwarding (CEF) is an advanced layer 3 switching technology used mainly in large core networks to enchance the network performance.
Let’s see how we can configure Cisco Express Forwarding (CEF) on cisco devices :
SWITCH_A(conf)#ip cef (CEF is already active on default config) SWITCH_A#show ip cef vlan 200
In some cases we can’t use Cisco Express Forwarding (CEF) :
1- IP headers that have options ( For security reasons )
2- For packets which has no TTL
3- Packets target to tunnel interface
4- Unsupported encapsulations
5- Packets requires fragmantation
*** CEF informations are kept in FIB ( Forwarding information base )