Successor vs Feasible Successor

mzinz

I thought I understood Successor's and Feasible Successor's until I read something out of my BSCI book:
"To qualify as a feasible successor, a next-hop router must have an AD less than the FD of the current successor route"

And if I understand things correctly:
AD = Cost of all hops to destination added, starting at next hop.
FD = Cost of local router to next hop.

What situation would have the cost of an entire route be less than the cost of the first hop of the current route?? Am I understand this wrong?

Spur

The answer lies in this forum

http://www.techexams.net/forums/viewtopic.php?t=21003

Good luck with your CCNP!

Sa'ad

AD is from your neighbor( next hop ) to the destination.
FD is from the current router, all the way to the destination, this would include all other routers in between your router and the destination.

Here is an illustration.


FD

---

AD

---

Destination.
R1

---

R2

---

R3


I hope that helps.

marlon23

"To qualify as a feasible successor, a next-hop router must have an AD less than the FD of the current successor route"

note : This condition is actually preventing routing loops.

mzinz

Thanks guys, that was really bugging me.

And thanks for the link to the other post, I didn't see that!