On linecards, what is "centralized forwarding", "local forwarding" ?

[Soon Kwan Kwon]

Hello all,

No matter I search about CFC, DFC, MSFC, PFC, SP&RP ..., I don't still understand clearly because there are difficult terms...

The question I want to know is below.

1. Centralized forwarding

On Cisco documentation, there is a sentence "CFC is centralized forwarding car."

I want to get more specific information.

2. Local forwarding

On Cisco documentation too, there is a sentence "CFC does not implement Local forwarding"

Please tell me more information.

3. DFC is subject to the same centralized performance characteristics of all other centralized forwarding modules, i.e., 30 Mpps maximum for the whole system.

Hoo.,.. Please tell me more information guys!

I look forward seeing your answers!!

Regards,

SK.

[Vinit Jain]

With Centralized forwarding, the forwarding decisions are made by the Supervisor engine (RP and the SP). On CFC cards, all the hardware programming or CEF related information is maintained on the supervisor engine. Where as on the DFC based cards, it has its own brain. i.e. When then system is brought up, the CEF is first programmed on the Supervisor card and then the CEF information is downloaded on the DFC (daughter card). This way, the lookup for the transit packets is not done by the supervisor but done by the DFC card itself. Only in cases where the packets is destined locally to the router or a recirculation of the packet (double lookup) is required, it is only when the packets are punted to the supervisor card by the DFC cards.

Hope this clarifies.

Regards

Vinit

[Soon Kwan Kwon]

Thank you so much concentrating to me.

Now, I've continuously tried to understand all terms related to CISCO backbone.

If I have a question, I'll post on this place.

Regards,

SK.

[Soon Kwan Kwon]

sir, I have a question.

I'm so so confused...ㅠ_ㅠ

I know CFC has CEF, while DFC has dCEF.

But, I just found that CEF uses a FIB to make IP destination prefix-based switching decisions.

It means that CFC also use FIB. -> Can CFC do local forwarding????? 

I'm so confused, please teach me what I misunderstand.. sir

Regards,

SK.

[Vinit Jain]

Hello Soon,

CFC can forward the packets but the forwarding decision is not made by Policy Feature Card (PFC) on the supervisor. CFC does not do local forwarding.

I would recommend referring to the below link for more details and understanding:

https://supportforums.cisco.com/document/85621/understanding-msfc-pfc-and-dfc-roles-catalyst-6500-series-switch#Introduction

Regards

Vinit

[Soon Kwan Kwon]

Thank you Vinit.

Maybe can we decide which one is the better performance and high price between CFC and DFC?

I think DFC is more better compared all of sides..

I don't know why CFC is existed..? CFC do not forward packets.. there's no need to use it..

Instead of CFC, I think I use DFC!!..

Why people use CFC..?

Ah.. I have a lot of question. 

Even though it is troublesome for you, please answer my question !! please

Regards,

SK.

[Vinit Jain]

DFC would be better performance wise but would be a bit expensive than the CFC card. The additional cost is for the daughter card that gets installed onto the linecard which makes it a DFC based card.

I would say, based on your environment, traffic and scale you can make a decision on which type of card to go for.

Hope this answers your query.

Regards

Vinit

[Soon Kwan Kwon]

Thank you so much Vinit!!!

It's really last 3 question.

If you answer these, I understand perfectly.

Can you see the things that I understand clearly?

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1. CFC can forward packets because it has CEF that uses FIB table.

but can't do local forwarding, it is done by PFC

right?

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2. Centralized forwarding is original packet forwarding?

right?

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3. Seeing your URL, I found below sentence!

Though the switch fabric is used for the data, but the CFC is responsible to send a look-up request from the Supervisor and then get those results back.

what is meaning "look-up request"?

What information do supervisor request to CFC ?

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Always thank you ㅠ_ㅠ

Regards,

SK