Cr-Lsp Backup; Fast Reroute - 3Com MSR 50 Series Configuration Manual

1356 C 77: MPLS TE C
HAPTER

CR-LSP Backup

Fast Reroute

ONFIGURATION
Automatic bandwidth adjustment of MPLS TE fulfills this function. It can
dynamically tune TE tunnel bandwidth based on measured service traffic.
CR-LSP backup provides end-to-end path protection for the entire LSP without
time limitation. This is different from fast reroute (FRR) which provides quick but
temporary per-link or per-node protection on an LSP.
In the same TE tunnel, the LSP used to back up a primary LSP is called a secondary
LSP. When the ingress of a TE tunnel detects that the primary LSP is unavailable, it
switches traffic to the secondary LSP and after the primary LSP becomes available,
switches traffic back. This is how LSP path protection is achieved.
Two approaches are available CR-LSP backup:
Hot backup where a secondary CR-LSP is created immediately after a primary
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CR-LSP is created. MPLS TE switches traffic to the secondary CR-LSP after the
primary CR-LSP fails.
Standard backup where a secondary CR-LSP is created to take over after the
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primary CR-LSP fails.
This section covers these topics:
"Overview" on page 1356
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"Basic concepts" on page 1356
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"Protection" on page 1356
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"Deploying FRR" on page 1357
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Overview
Fast reroute (FRR) provides a quick per-link or per-node protection on an LSP.
In this approach, once a link or node fails on a path, FRR comes up to reroute the
path to a new link or node to bypass the failed link or node. This can happen as
fast as 50 milliseconds thus minimizing data loss.
Once a link or node on an LSP configured with FRR fails, traffic is switched to the
protection link and the headend of the LSP starts attempting to set up a new LSP.
Basic concepts
The following are concepts that FRR involves throughout this document:
Primary LSP: The protected LSP.
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Bypass LSP: An LSP used to protect the primary LSP.
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Point of local repair (PLR): The ingress of the bypass LSP. It must be located on
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the primary LSP but must not be the egress.
Merge point (MP): The egress of the bypass LSP. It must be located on the
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primary LSP but must not be the ingress.
Protection
FRR provides link protection and node protection for an LSP as follows: