thanks a alot Jon!

Usually fib table contains:

prefix,next hop outgoing interface.

question is how can switching engine on line card store informations such as source ip, layer 4 ports, in fib table as there is no such field(port number,source ip)?

Does it mean Fib structure in acef is different from fib structure in dcef in terms of what kind of informations ,they could hold?

thanks a lot!

Thanks a lot Jon!

Sarah, in summary, MLS does all the L3 analysis with the first packet of the flow, and forwards subsequent packets of the flow using L2 hardware.

If you want to become more familiar with Cisco's MLS you might look at some Cisco documentation on the 5500 series. On those, it required extra hardware and manual configuration, so the supporting explanations are better, I think, then what you find in reference to MLS with the 6500 series.

What might make this especially clear, if you read about how a 5500 L2 switch could cooperate with an external L3 router to perform MLS.

Giuseppe, reading your post, my post must seem misleading; and perhaps it was since I didn't provide much context.

I was trying to expand upon the functioning of aCEF using MLS, not CEF vs. process switching, CEF vs. other caching techniques (your mention of Fast switching), or the difference between 5500 MLS and 6500 1st packet physical processing, or 6500 using line cards with a DFC performing dCEF.

If you read the aCEF reference Jon supplied, you'll see how the first packet is directed to sup720, which in turn caches the flow to switch subsequent packets of the same flow without incurring the lookup overhead on the PFC3. This appears somewhat similar to 5500 MLS, logically, as it was performed on the 5500 series. I.e. routing first packet, switching subsequent packets. The reference document isn't clear where the aCEF cache-based forwarding actually takes place.

I was also trying to expand upon the concept of MLS itself, which I think is better explained in the 5500 documentation, vs. CEF. The primary purpose of CEF being processing the 1st packet as quickly as subsequent packets.

Hello Joseph,

I've read the ACEF reference.

I agree this is an hybrid model of MLS with forwarding caching performed on capable modules.

I think this is the best approximation to distributed CEF that is available for a C6500 in Hybrid Mode.

It has two levels of caches: PFC3 has a complete CEF table populated by MSFC, the capable modules query it and cache the results: the first packet is processed in the main CEF table not by a route processor.

It says the first packet is sent to PFC3.

The HW components are:

Supervisor Engine 720 with the integrated 720 Gbps switch fabric

•Supported switching modules:

-48-port 10/100/1000BASE-TX (WS-X6748-GE-TX)

-24-port 1000BASEX (WS-X6724-SFP)

-48 port-1000BASEX (WS-X6748-SFP)

-4-port 10-Gigabit Ethernet (WS-X6704-10GE)

These are all modules that should support DFCs in Native IOS as they are in the newest series.

The purpose of this strategy is to leave the PFC3 free to help less powerful modules in the chassis.

Sorry for my previous post actually it is a little change on what you said.

Hope to help

Giuseppe

Giuseppe, nothing for you to be sorry for. If my post wasn't clear in the point I was trying to make, the fault is mine.