EIGRP load balancing 5:1 ratio

Unanswered Question
Jun 15th, 2009

Hi, I have Router R1, R2 & R3. Router R2 has Network 10.10.10.0/24. All are in Eigrp domain. From R1, we have two path to reach reach 10.10.10.x subnet. R1->R2 (Directly) & R1->R3->R2. I have to share data on 5:1 ratio, how we can do it.

R1(S0/0->256kbs)-> R2 (S0/0->256kbs)

R1(S0/1->1.536Mbs)-> R3(S0/0->1.536Mbs)

R3 (S0/1->1.28Mbs)-> R2(S0/1->1.28Mbs)

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Replies

Giuseppe Larosa Mon, 06/15/2009 - 23:14

Hello Rupesh,

EIGRP metric with default K values is proportional to the sum of delays (in tens of microseconds 1 msec = 100 tens of microseconds) and to the inverse of the lowest BW in path expressed in kbps.

path1 = 256 * (Delay of s0/0 in tens of microseconds) + 256 * 10^7/256

path2 = 256 * (Delay_R1_s0/1+ Delay_R3_s0/1) + 256 * (10^7 / 1280)

lowest BW on path 2 is 1280 kbps.

you can get the delay parameters from

sh int serx/y on the routers.

The best path is path2, path1 provides a feasible successor so you can use the variance command

R1:

router eigrp xx

variance 6

you may need to tune the interface parameters delay and BW to get a 5:1 ratio between the two metrics.

Hope to help

Giuseppe

Rupesh Kashyap Tue, 06/16/2009 - 01:51

Now I have two qn-

1. Ration is 5:1, so Variance will 5 or 6

2.path2 = 256 * (Delay_R1_s0/1+ Delay_R3_s0/1) + 256 * (10^7 / 1280)

lowest BW on path 2 is 1280 kbps.

It means, no role of delay from R1-R3 or no bandwidth considered from R1-R3. Please help me as I am trying to find the solution for last 2 months. You would be like GOD for me.

Rupesh Kashyap Tue, 06/16/2009 - 02:33

Hi, I did it, but load is sharing as 60:13. One thing more, why we have selected 1280Kbs via R1-R3-R2, why we have ignored 1536Kbs ? The only problem is I am not getting exact 5:1.

Rupesh Kashyap Tue, 06/16/2009 - 02:56

GOOD News...

Finally I found it. I have only one qn now. We have 1536kbs between R1-R3 & 128Kbs between R3-R2. Why we have considered lower one. What about if we reverse the bandwidth I mean R1-R3->128Kbs & R3-R2->1536kbs, then which one I have select in path 2 ?

Giuseppe Larosa Tue, 06/16/2009 - 05:03

Hello Rupesh,

>> Why we have considered lower one.

This is the way EIGRP metric works:

cumulative in delay

inverse proportional to lowest BW in path. = 10^7/Lowest_BW [kbps]

EIGRP route data structure a TLV (type length value) contains separated fields for all the metric components + the minimum MTU on path.

R1 can easily calculate the path metric from its own point of view by adding link delay to reported distance = received metric fields and by comparing the BW on the link with the BW field value.

see

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a00800c2d96.shtml

Hope to help

Giuseppe