When an LSP is switched from an existing working path to a new path, it is desirable to perform this in a hitless fashion. The Make-Before-Break (MBB) procedure consist of first signaling the new path when it is up, and having the ingress LER move the traffic to the new path. Only then the ingress LER tears down the original path.
MBB procedure is raised during the following operations:
timer based and manual re-signal of an LSP path
Fast-ReRoute (FRR) global revertive procedures
Traffic-Engineering (TE) graceful shutdown procedures