H3C Technologies H3C S7500E Series Switches - Manual (Page 93)

3-11
CR-LSP Backup
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 for CR-LSP backup:
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Hot backup where a secondary CR-LSP is created immediately after a primary CR-LSP is created.
MPLS TE switches traffic to the secondary CR-LSP after the primary CR-LSP fails.
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Standard backup where a secondary CR-LSP is created to take over after the primary CR-LSP
fails.
Fast Reroute
This section covers these topics:
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Overview
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Basic concepts
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Protection
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Deploying FRR
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:
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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 the primary LSP
but must not be the egress.
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Merge point (MP): The egress of the bypass LSP. It must be located on the primary LSP but must
not be the ingress.
Protection
FRR provides link protection and node protection for an LSP as follows:
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Link protection, where the PLR and the MP are connected through a direct link and the primary
LSP traverses this link. When the link fails, traffic is switched to the bypass LSP. As shown in
Figure 3-4 , the primary LSP is Router A → Router B → Router C → Router D, and the bypass
LSP is Router B → Router F → Router C.