eigrp formula...again

[jimfixit]

Grr sometimes I have this big block on my head. Math wasn't my strongest suit ever...

I understand the EIGRP forumla to calculate FD. BUT my situation is I need to come up with the values for bandwidth and delay such that, when load balanced, the ratio = 3.4.

For the life of me I can't make this happen. The closest I can get is 1.9. That won't cut it. I have to balance an OC3 with a DS3 (yeah okay I know). For the price we are paying for that DS3 they want SOMETHING to be going over that link.

So, you have FD1/FD2 = 3.4

You explode the calcualtions for FD1 and FD2

256(10^7/bw1+(delay1/10)) / 256(10^7/bw2+(delay2/10))=3.4
you multiply both sides by the FD2 formula:
256(10^7/bw1+(delay1/10))= 3.4 * 256(10^7/bw2+(delay2/10)))

and then...what? no matter what you do you are going to keep solving for one value in terms of the other, which doesn't exactly help.

I set up a spreadsheet to run the numbers so that I could plug in values for each of the bandwidths and delays, and...the best ratio I can get is 1.9. I think if I balance OC3 and DS3 at that ratio, I'm going to overrun that DS3.

Egads what do real people do for fun???!

 

[brianinms]

Have you considered using the bandwidth command on the interface to influence the calculations?

 

[jimfixit]

bandwidth and delay both. That's the problem. The 'real' values because of the feasibility condition, appear to be a loop because there is so much disparity between them.

I have worked up a spread sheet where I can plug in the values for these formulas but it will never give me better than 1.9 ratio without violating the FC and, EIGRP will round 1.9 down so that we get a 1 to 1 load balance. No help there at all.

Thanks

 

[lerdalt]

Try this for your calculations
bw1 = 58
delay 1 = 1
bw2 = 200
delay 2 = 1