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Advanced MPLS/RSVP Features
Make-Before-Break (MBB) Procedures for LSP/Path Parameter
Configuration Change
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:
1. Timer based and manual re-signal of an LSP path.
2. Fast-ReRoute (FRR) global revertive procedures.
3. Soft Pre-emption of an LSP path.
4. Traffic-Engineering (TE) graceful shutdown procedures.
5. Update of secondary path due to an update to primary path SRLG.
6. LSP primary or secondary path name change.
7. LSP or path configuration parameter change.
In a prior implementation, item (7) covers the following parameters:
1. Changing the primary or secondary path bandwidth parameter on the fly.
2. 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:
1. Changes to include/exclude of admin groups at LSP and path levels.
2. Enabling/disabling LSP level cspf option.
3. Enabling/disabling LSP level use-te-metric parameter when cspf option is enabled.
4. Enabling/disabling LSP level propagate-admin-group option.
5. Enabling/disabling LSP level hop-limit option in the fast-reroute context.
6. Enabling the LSP level least-fill option.
7. Enabling/disabling LSP level adspec option.
8. Changing between node-protect and "no node-protect" (link-protect) values in the LSP
9. Changing LSP primary or secondary path priority values (setup-priority and hold-
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level fast-reroute option.
priority).
7950 SR OS MPLS Configuration Guide
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