How CEF uses the FIB and Adjacency table.

[nsnelson402]

Hello,

I'm studying for my CCNP route and I was wondering if someone could confirm that the understanding I have of CEF and how it uses the FIB and Adjacency table is somewhat accurate.

CEF uses the FIB and adjacency table to encapsulate and forward packets. It determines what the next hop IP address is for the destination prefix using the FIB, then correlates that next hop IP address to an adjacency table entry where it finds the MAC addresses to use for encapsulating the packet.

Is this right? I've been digging through all kinds of white pages for awhile and this is the picture I have.

[Jon Marshall · Accepted solution]

Yes you have it right.

CEF uses a FIB which is an optimised lookup table (an mtrie structure) with pointers to entries in the adjacency table.

You may want to have a read of the following chapter from the CCIE V5.0 certification guide one of whose authors, Peter Paluch, is a regular poster on these forums, and it should clear up any remaining questions you have -

http://www.ciscopress.com/content/images/9781587143960/samplepages/9781587143960.pdf

by all means post back here though if you have other questions.

Jon

[nsnelson402]

Thank you for the confirmation. Also thank you for the reference that helped make things pretty clear.

Regards,

Nick