Brocade Multi-Service IronWare Multiprotocol Label Switch (MPLS) Configuration Guide (Supporting R05.6.00) - Manual (Page 214)

190 Multi-Service IronWare Multiprotocol Label Switch (MPLS) Configuration Guide
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RSVP LSP with FRR
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RSVP LSP with FRR
RSVP LSP with FRR (fast reroute) protection can use two different protection methods. This
documentation will use the terms of detour backup and facility backup going forward for
differentiation. Detour backup establishes backup path with detour sessions from PLR (point of
local repair) to MP (merge point) while Facility backup uses bypass LSP as tunnel to establish
backup path from PLR to MP. This feature focuses on the algorithm of facility backup path
computation and allows you to change from existing very restricted qualification criteria of selecting
bypass LSP to much relaxed set of criteria.
This feature is disabled by default and Bypass selection or Dynamic bypass creation for a backups
is as per existing selection mechanism. When the user enables liberal bypass option, new Bypass
selection, or dynamic bypass, creation comes into effect.
TABLE 12
Term Meaning
FRR, Protected LSP RSVP Fast Reroute enabled LSP.
PLR FRR Point of Local Repair. Can be any node along Protected LSP path, except egress.
MP FRR Merge Point. Can be any node along Protected LSP path, except ingress.
Backup Path Facility backup FRR protecting path from PLR to MP.
Bypass LSP LSP tunnels used by Backup paths for Facility backup FRR. Backup Paths Ride on Bypass
LSP from PLR to MP. Bypass LSP provides N:1 FRR protection.
Static Bypass User created Bypass LSP.
Dynamic Bypass Bypass LSP which are created on demand, if there are no existing bypass LSPs satisfying
backup Path constraints.
Backup Selection Mechanism in which a protected LSP selects a Bypass LSP for its backup path at a PLR.
RSVP bypass LSP terms
Specifications
RSVP FRR LSP with detour backup or facility backup applies the same algorithm for backup path
computation. The algorithm is designed to follow RFCs to avoid various issues intrinsic to detour
backup type such as early session merging and bandwidth sharing. Because bypass LSP provide
virtual tunnel to isolate the visibility of backup sessions and protected session, most of those
issues are not present in the facility backup mode. Applying the same algorithm in the facility
backup as in detour backup computation is to be very conservative. The only benefit of using the
current conservative algorithm is to prevent a single failure triggering both the protected session
and backup session failures at the same time. The restrictive algorithm can run into situations that
no backup path can be established due to bypass LSPs cannot qualify under those restrictions,
especially under certain less meshed topology such as single ring topology.
The steps of facility backup path computation, which involves selecting best qualified bypass LSP
are:
Merge point selection: PLR backup query process first selects in the order of preferred merge point,
based on ingress signaled property. Once a merge point is selected in the order of preference, it
selects from the available bypass LSPs reaching this merge point. If no bypass LSP qualify to serve,
it moves on to the next preferred merge point. The merge point preference order depends on if
ingress signal with the node protection has the desired flag.