EIGRP - How to ignore Feasibility Condition?

Unanswered Question
Aug 10th, 2009

Hi guys!

I was making some labs regarding EIGRP. One of the goals of this lab was to make a load balancing between two paths. The problem is that only one path was in the topology table due the FC (Feasibility Condition). So, I could not use variance since there was only on route on Topology Table.

I found two ways to solve this, as a work around.

The first one is to create a route-map and subtract the metric then using variance command. The other one is very similar, but using off-set to subtract the metric and then use the variance in the same way of the first option.

Anyway, these workarounds do not really solve the issue because the goal of this lab is to make load balancing, but by turning off FC. According to I heard, it is possible, but I could find nothing.

Does someone know about that? Is that possible to turn off or bypass/ignore the FC?

I heard that it is possible just inserting a specific command...

Thanks in advance.

I have this problem too.
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ronaldobf Mon, 08/10/2009 - 18:19

I just forgot to say:

- All Ks were enabled intensionally in order to match the FC on this specific lab;

- All interface bandwidths are set properly;

- I can not change the options above.

Regards

Ronaldo Bueno Filho

Peter Paluch Tue, 08/11/2009 - 00:24

Hello,

As far as I know, you cannot force EIGRP to ignore the feasiblity condition. The feasibility condition is a fundamental issue in the EIGRP algorithm as it provides protection against routing loops and controls when a diffusing computation should start or be propagated further. The feasibility condition is an intrinsic part of the entire algorithm and even if it could be deactivated, it would disrupt the operations of the EIGRP protocol.

A feasibility condition for a particular route and a particular neighbor is met when the reported distance by that neighbor is lower than our feasible distance, i.e., when RD < FD. Note that you cannot change the RD by changing any of the EIGRP metric parameters on your links because they do not influence the distance as reported to you by your neighbor. Therefore, the only options left for you are indeed metric manipulations via offset lists. I am not sure about route-maps - they are usable in redistribution but on my 12.4 IOS, there is no possibility in using route-map for metric manipulation within the EIGRP protocol.

Best regards,

Peter

ronaldobf Tue, 08/11/2009 - 15:10

you're right regarding the route-map. I just forgot to say that the use of the route map is under redistribution proccess, as you can see below:

R3(config-route-map)#set metric ?

+/- Add or subtract metric

<0-4294967295> Metric value or Bandwidth in Kbits per second

Regarding the FC, I agree with you that it is part of EIGRP algorithm, but my friend told me that it is possible. He also gave me some documentation. However, that information is written indirectly so I could not find.

You are probably asking yourself "if he is your friend, and if it is possible to bypass the FC, why your friend is hiding that???"

The answer is that we make some labs (challenges) to each other and I just want to discover that before he tells me. :)

Thanks,

Peter Paluch Tue, 08/11/2009 - 22:42

Hi Ronaldo,

Personally, I do not know about any way how to "deactivate" the feasibility condition check. As far as I know, you can only make a route pass that check. If there is really a way how to disable the FC check I would be really interested in knowing about that (but then again, I would say it will make the entire EIGRP fall apart).

Can you perhaps post here the documentation your friend has given you, even if it is indirect?

Best regards,

Peter

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