- Cisco Employee,
Is it possible that an EIGRP router selects a sub-optimal route over an optimal route?
The cost is simplified for ease of calculation.
- Based on the above scenario, the best route to Network-A from R1 is through R2; therefore the Feasible Distance equals 11 (5 + 5 + 1 = 11).
- Only route from R1 to Network-A through R4 satisfies the Feasible Condition, and is installed in the Topology table.
- Route R1-R3-R5-Network-A is left out b/c it does not meet the FC, even though it has better metric to reach Network-A than through R4.
Now consider how R5 routes packet back to R1. The best path back to R1 is through R2 with FD = 10.
R5 also have 2 other routes back to R1 through R3 and R4, both of which satisfy the FC.
Let's say R2 fails, R1 would look into its topology table and select a backup route through R4 (the only backup route). R5 would do the same thing and select backup route through R3 (better metric). Would the result of this be an assymetric routing path from R1 - Network-A and back??? R1 - R4 - R5 - R3 - R1