If BIER Fast Reroute (FRR) is not enabled, when there is a failure on the primary next-hop BIER does not switch to the protection next-hop (LFA) even if one exists. After the failure, BIER waits for IGP to converge and a new next-hop to be available, which means that traffic interruption is equal to the IGP convergence time. LFA is still configurable when BIER is enabled and can be used for other IP and MPLS functionality.
If BIER FRR is enabled, BIER uses the available underlay Loop-Free Alternates (LFA) to provide link protection to neighbors and the recovery time from link failure is less than the IGP convergence time.