FIB Generation - is this correct?

UnixGeek

My understanding of the FIB is that it's normally generated by the Layer 3 Forwarding Engine after receiving the routing table from the Layer 3 Engine.

According to the BCMSN book that I'm reading, with Distributed CEF, the Layer 3 Engine generates the FIB.

Is either my understanding, or this book incorrect, or the second statement just an exception to the first?

szmarcek

Hi,


My understanding of that is that Layer 3 engine builds FIB (from routing table) and adjency table (from ARP table) and then they are used by Layer 3 forwarding engine to forward traffic in hardware. However, I may be totally wrong about that so perhaps someone more knowledgeable can post.

APA

With dCEF

1) Layer 3 Engine (Route Processor\MSFC) - Creates the FIB from route table and adjacency table from (CAM\ARP table)

2) Layer 3 Forwarding Engines receive a copy of the FIB and Adj-Table from the Layer 3 Engine to use in packet fowarding.

3) Layer 3 Engine has no need to be interrupted for packet fowarding as the FIB\Adj-Table has been distributed to the Layer 3 Forwarding engines for them to autonomously forward packets via hardware switching.

I'm certain this is how dCEF operates.

networker050184

I have the same understanding as APA. I've been meaning to read Inside Cisco IOS Software Architecture for a while, but just haven't had the time.

kryolla

I thought dCEF happens at the line cards for traffic that doesnt leave the line cards and for traffic that has to go to another line card then it gets regular cef switched. I guess the layer 3 forwarding engines are at each line card. Its too early for this and I havent had my coffee yet

UnixGeek

Thanks everyone. If we take dCEF out of the equation, and just look at vanilla CEF, which component generates the FIB?