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EIGRP and Load Balacing Per Packet CEF required on both ends???

Here's what I have.

-2 T1's with same EIGRP metric

-CEF is enabled and load sharing currently

1 Link is being used more than the other due to nature of load sharing and not per packet using CEF.

I need per packet setup to see if this improves performance and distributes the usage over both links effectively.

If I enable per-packet on my remote office, do I also have to enable it on each PVC that connects back to my central office per PVC. Or can you enable per packet on the remote location only and be ok? I dont have control over central office router and need to justify if I need to enable that on the Central office or not.

Cisco docs I reviewed on this doesn't say both ends.


Re: EIGRP and Load Balacing Per Packet CEF required on both ends


If you want the traffic to be process switched (per-packet basis) in both directions then it has to be enabled on both ends. Switching type configured on an ingress interface only applies to the local device/interface and has no control over return traffic. Also, keep in mind process switching can cause the CPU utilizaton to go up.

Hope that helps!



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Re: EIGRP and Load Balacing Per Packet CEF required on both ends

I agree with Sundar's point about needing to configure both ends if you want to use per packet in each direction. His point about the implications of forcing process switching and its impact on CPU utilization of the router is true but I am not sure that is what the original post was asking about. As I understood the original post he was asking about the per-packet option available with CEF switching which does not produce process switched packets.

I have one caution to offer about turning on the per-packet option with CEF. If you do that you will probably get better - but still not even - balancing of the serial links. But the performance may not improve. In fact it may degrade. This is because doing per packet balancing introduces the liklihood of out of order packets. The impact of out of order packets varies depending on the application being run and the impact of out of order packets. Many applications when they get an out of order packet will discard the packet and retransmit packets to get them in the correct order. I actually know of one customer site where they enabled per packet balancing and the performance of the application got worse. So I suggest that you evaluate carefully the implications of per packet balancing.



Community Member

Re: EIGRP and Load Balacing Per Packet CEF required on both ends

Great responses guys. Richard thank you for your insight. We have another customer that terminates on a colocation router in our hosting facility and they have it setup at both ends. So far I have not heard of any issues with it. I suppose if its not setup on one end you still have the potential for load balancing problems on return. Also you mentioned that it may degrade too depending on how the application responds.....guess Ill have to make sure the application doesn't react and cause more of an issue. Another customer that works fine on it using same application, web based database connectivitiy.....dunno. Hard to decided what to do at this point. Can't really go with Multilink PPP as not a design option on the core. This appears to have been the best option available.

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