Hello Luis
FRR employed in EIGRP is a mechanism by which the feasible successor is already installed in the routing table to speed up the installment of the alternate path during reconvergence after a failure. But in order to speed up the installment, it is also necessary to speed up detection. FRR uses multiple methods by which this speedy detection is achieved, and one of them is BFD.
Note here that FRR is a mechanism that is fully described in RFC 5714 and is applicable not only to EIGRP, but to most conventional IP routing protocols. Specifically, it states:
It is critical that the failure detection time is minimized. A
number of well-documented approaches are possible, such as:
- Physical detection; for example, loss of light.
- Protocol detection that is routing protocol independent; for
example, the Bidirectional Failure Detection protocol [BFD].- Routing protocol detection; for example, use of “fast Hellos”.
FRR for EIGRP creates a BFD session in order to quickly detect failures. You don’t actually have to configure BFD in order for it to operate here, but it is an underlying mechanism of the FRR functionality. For other routing mechanisms, such as MPLS for example, what is known as “BFD Triggered FRR” must be manually configured.
I hope this has been helpful!
Laz