network cisco ccna gns3 certification arteq

network cisco ccna gns3 certification arteq
a network runs through it

Search insearchofthecert

Tuesday, July 10, 2012

ine on k values for eigrp...

outstanding article by marko... damn... read the whole thing...

I don’t know about all you guys out there, but I was taught as a CCNA that when you redistribute into EIGRP you have to “set your K-Values.” This leads people to think that the numbers you enter during redistribution ARE the K-Values when in fact they are not. The numbers we enter here are simply values of which SOME are used in the calculation of the final composite metric. IF I was indeed inputting the value of K1 here on the first line, how could it possibly be a range between 1 and 4294967295 if a K-value by definition is an integer between 1 and 255? The answer is it can’t.
We are not specifying a K-Value. We are specifying the bandwidth variable used in the metric calculation. That value will in fact be MULTIPLIED by whatever value has been set for K1. I said SOME of these entered values are used in the calculation of metric. The reason I say SOME is because of the 5th and final value entered in the redistribution metric above. Take a look at the IOS help. It instructs us to enter the MTU of the path. Again, when people are under the impression that they are entering K-values here, it leads them to mistakenly believe that the 5th thing they enter must be K5 and therefore K5 must be equal to MTU. This is not true either. What we are entering here is indeed a value for MTU.
The MTU however is not used at any point during the calculation of the metric. Take a look at our full formula again.
EIGRP Metric = 256*((K1*Bw) + (K2*Bw)/(256-Load) + K3*Delay)*(K5/(Reliability + K4)))
Where in that formula do we see MTU? Nowhere. It simply does not exist in the calculation. So why do we enter it then? Because MTU is actually carried in EIGRP packets. It just has nothing to do with metric calculation. We keep saying that K-Values are just integers between 1 and 255 right? If we do not specify them during redistribution, where DO we? Under the EIGRP process using the “metric weights” command. To further illustrate the fact that MTU has nothing to do with metric calculation in EIGRP, let’s go ahead and set K5 = 1 on both sides.

No comments:

Post a Comment