When soft preemption is not enabled for the P2MP LSP, the value of the preemption timer is hard coded as 0 for S2L LSPs. That is, S2Ls are hard preempted by higher priority LSPs. Make-before-break (MBB) is not performed at the root of the preempted S2L. That is, the S2L is immediately torn down to the root PE when it is preempted and must signal again.
When an S2L is preempted, it sends an RESVTEAR message to the root PE (head-end) indicating the lack of resources, and then the S2L is torn down throughout the network. After the P2MP S2L retry or fast retry timer expires, the S2L signals again by sending a new PATH message from the headend, based on the newly calculated Constraint-based Shortest Path First (CSPF) path where the bandwidth resources are available.
S2Ls can preempt other P2P LSPs or other S2Ls based on the hold and setup priority.