EIGRP traffic engineering with delay modification

Note: I have modified the metric weights so that delay is the ONLY value used to calculate the composite metric.

First off, lets check to see what R4's EIGRP topology table shows for R3's loopback (3.3.3.3/32)...

As we can see here, R4 has equal costs via R1 and R2. We can also see that the total delay is currently 5200 microseconds, or 520 10s of microseconds. This is useful, as the delay calculation is 256*10s of microseconds, or 256*520 = 133120. We can also take the reported distance (delay calculation as advertised from our peer) to determine that both R1 and R2 have a delay value of 510 10s of seconds, or 5100.  

Now, say we wish to modify the path so that the preferred path from R4 is through R2, exclusively. We can shoot from the hip, and crank R1's delay to the moon (99999), or try and figure out what value we can configure so that the path will remain as a feasible successor. If we make the modification on R1, we will increase both the feasible distance as well as the advertised distance from R4's perspective. Unfortunately, if we crank the value up too high..it won't be a feasible successor. So the goal here is that we modify the feasible distance high enough, but not enough so that the value is greater than or equal to 133120.  

BAM! We increased the delay value on R1's fa1/0 interface to 11 10s of microseconds..or 110. With previous value of 100, we now see a total delay via R1 to be 5210 versus the 5200 via R2. By only increasing the delay by a marginal amount, we've successfully maintained R1 as a feasible successor, yay!

**********************Previous configurations removed**********************

What would have happened if we were to modify the delay value on R4’s fa0/0 interface?  Would we see the FD and the RD increase, or just one or the other?  Well, since the RD is what is “reported” to us from our neighbor, the value will stay the same.  Since we are modifying our local delay value, the FD will increase for both paths.  This might be a possible solution if we were to have two separate paths…but in this scenario it is a shared segment..so there will be no path changes.

**********************Previous configurations removed**********************

What happens if we increase the delay value on R1’s fa0/0 interface?  What will happen?  For sake of clarity, lets crank it up to 9999999.

As you can see, there is no change....From R4's perspective. But if we were to look at R3, it wouldn't see R1 as a feasible successor.