Notebook – CEF

CEF - Cisco Express Forwarding
-Both routers and Layer 3 switch both have IOS routing software.
-Software Routing is slow compared to ASICs
L3 switching can use a software and hardware method to move data.
FIB - Fowarding Information Base - Caches Routing Information from the Router supervisor
ADJ Table "routes" (fowards) frames out a port based on mac address information.
ASIC is a name for a switches hardware.
CEF takes L3 routing informaion and caches it to the FIB.
As the switch is booting up, it will look for all the next hop addresses in the routing table
 and pull the MAC addresses from the addresses.
This information is then sent to the adjacency table with all the necessary ARP information.
CEF only tracks routed ports (or interface vlans)
Exceptions to CEF:
Packets with Header options
Packets with TTL expired
Packets destined to use tunnel interfaces
Packets with unsupported encapsulations
Packets required fragmentaion (MTU Exceeded)
to turn on CEF:
switch(config)#ip cef
CEF has a feature to watch all traffic statistics.
Will only work for routed interface vlans

show ip cef vlan 200:
shows what ips have been learned by CEF in vlan 200.
ex output:
switch#show ip cef vlan 151
 attached to Vlan151
The was learned on vlan 151
switch#show ip cef

show ip arp x.x.x.x
shows arp information for the specified IP address, and what interface it was learned on.

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