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Community Member

PBR on 881

Hello All,

I have a question if PBR runs on hardware (CEF switched) on an ISR 881 router.

My intent is to use PBR on an SVI on ISR 881.

6 REPLIES
VIP Super Bronze

PBR on 881

Purple

PBR on 881

Hi Reza,

Where in this doc do you see that PBR is not CEF switched ? To my best knowledge it's been a while now that PBR is having CEF support, ain't it ?

Regards

Alain

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Don't forget to rate helpful posts.
Cisco Employee

PBR on 881

Hi,

ISR 881 is software based router. Nothing is hardware switched. As Alain mentioned, PBR is CEF switched, but still prcoessed by the CPU.

HTH,

Lei Tian

Community Member

Re: PBR on 881

My problem is that I need to provide full tunnelling for the dmvpn users behind ISR 881. Is PBR a good option? Is it not gonna kill the router's CPU? My understanding is if Cef is enabled then it should not affect CPU load at every packet, only at the first ones.
Thanks

Sent from Cisco Technical Support iPhone App

Hall of Fame Super Gold

PBR on 881

Depending on what you exactly need to do, PBR may not even be needed.

As Lei correctly indicated above, CEF is totally software based on this class of routers. CPU will process every single packet.

Hall of Fame Super Gold

PBR on 881

There are subtle aspects to the question and its answer and we need to be careful in how we understand them. It is absolutely true that this class of router forwards everything in software and that every packet will be handled by the CPU, and therefore that every packet will contribute to CPU busy. However it is not the same as a process switched packet which can impose a higher load on the CPU. With CEF enabled the search of the forwarding table is made more efficient and the adjacency table already has the layer 2 rewrite data calculated. So the forwarding of a packet in CEF is much more efficient (lower CPU burden) than a process switched packet would be.

It seems to me that the original question really has two parts:

- hardware or software forwarding and the answer is software

- CEF or process switching and the answer is CEF.

We have no information about how many dmvpn peers, how many users, or how much traffic will be generated. These factors would need to be considered to determine whether the 881 is an appropriate platform for this deployment.

HTH

Rick

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