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 invoked during the following operations:
timer based and manual resignal of an LSP path
Fast-ReRoute (FRR) global revertive procedures
soft preemption of an LSP path
Traffic-Engineering (TE) graceful shutdown procedures
update of secondary path because of an update to primary path SRLG
LSP primary or secondary path name change
LSP or path configuration parameter change
In a prior implementation, item7 covers the following parameters:
changing the primary or secondary path bandwidth parameter on the fly
enabling the frr option for an LSP
This feature extends the coverage of the MBB procedure to most of the other LSP level and Path level parameters as follows:
changes to include/exclude of admin groups at LSP and path levels
enabling/disabling LSP level path-computation local-cspf option
enabling/disabling LSP level metric-type parameter
enabling/disabling LSP level propagate-admin-group option
enabling/disabling LSP level hop-limit option in the fast-reroute context
enabling the LSP level least-fill option
enabling/disabling LSP level adspec option
changing between node-protect and ‟no node-protect” (link-protect) values in the LSP level fast-reroute option
changing LSP primary or secondary path priority values (setup-priority and hold-priority)
changing LSP primary or secondary path class-type value and primary path backup-class-type value
changing LSP level and path level hop-limit parameter value
enabling/disabling primary or secondary path record and record-label options
This feature is not supported on a manual bypass LSP.
P2MP Tree Level Make-before-break operation is supported if changes are made to the following parameters on LSP-Template:
changing bandwidth on P2MP LSP-Template
enabling Fast Re-Route on P2MP LSP-Template