What is the purpose of CEF and the FIB and AT tables
Posted on 2010-09-03
My understanding of routers is that they can use Distributed CEF, CEF, Fast switching and Process switching.
Is the above routing or switching?
If you use CEF then you need a FIB and AT tables? No CEF then no FIB or AT?
A FIB appears to me to be a combination of the Route Table and the ARP cache.
The AT table is confusing but the name seems to imply it is similar to a mac-address-table.
I have tried reading about CEF many times but it is confusing because I don't understand the basics...The router starts off routing and then determines distinct flows of data and then starts switching using CEF?
If a Router does not have CEF then no FIB and AT and all packets are Routed but not switched?
I have looked at the FIB using the show ip cef and it makes sense but when I try to look at the AT table it appears blank or does not make sense to me. Maybe I am running the wrong command; I have ran something like sh ip cef adjacencies or something similar.
Is CEF just offloading the routing from the CPU to the switching ASICS?