Ok, I still have some problem understanding the FD and the AD from any router to a given network:
For explaining I am taking the below example:
The network 137.72.128.31 /32 is the loopback 0 address of the RouterA interface:
I do a show topology table for this IP and get the below information
The router has calculated a FD to it's own IP and given the value which is perfectly correct
RouterA#sh ip eigrp topo | b 137.72.128.31/32
P 137.72.128.31/32, 1 successors, FD is 128256
Here is how the calculation was done:
RouterA#sh int lo 0 | in BW
MTU 1514 bytes, BW 8000000 Kbit, DLY 5000 usec,
RouterA#
This gives us the formula:
(10^7 / 8000000 + delay ) * 256
(1.25 + 500) * 256
(1 + 500) * 256
501 * 256
128256
The above calculation works perfect and gives the FD as 128256. So RouterA has calculated a metric to it's own directly connected network.
Till this part I am clear but here is where my confusion starts.
Consider RouterA is connected to RouterB with a link of bandwidth 2 Gig. Now the FD from RouterB to the loopback 0 interface of RouterA should be the AD that RouterA advertises(that means it's own FD) plus the Metric that RouterB calculates on it's own.
Now this is how RouterB calculates it metric:
RouterB#sh int po 1 | i BW
MTU 1500 bytes, BW 2000000 Kbit, DLY 10 usec,
RouterB#
The least BW is 2Gig(2000000 Kbit) and the delay would be 5000 + 10=5010
This gives us the formula:
(10^7 / 2000000 + delay) * 256
(5 + 501) * 256
506 * 256
129536
As per my understanding, from the above the FD calculated by RouterB to loopback interface of RouterA should actually be 129536 + 128256 = 257792
But the output shows this as 129536 which is the calculated metric of RouterB to the loopback interface of RouterA.
RouterB#sh ip eigrp topo | be 137.72.128.31
P 137.72.128.31/32, 1 successors, FD is 129536
So, now my question is where am I going wrong or is my understanding wrong on the FD part?
