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What is the purpose of CEF and the FIB and AT tables

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?
Switches / HubsRoutersNetwork Architecture

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Don Johnston

8/22/2022 - Mon