H3C Technologies H3C S7500E Series Switches - Manual (Page 94)

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Figure 3-4 FRR link protection
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Node protection, where the PLR and the MP are connected through a device and the primary LSP
traverses this device. When the device fails, traffic is switched to the bypass LSP. As shown in
Figure 3-5 , the primary LSP is Router A → Router B → Router C → Router D → Router E, and
the bypass LSP is Router B → Router F→ Router D. Router C is the protected device.
Figure 3-5 FRR node protection
Deploying FRR
When configuring the bypass LSP, make sure the protected link or node is not on the bypass LSP.
As bypass LSPs are pre-established, FRR requires extra bandwidth. When network bandwidth is
insufficient, you are recommended to use FRR for crucial interfaces or links only.
Link status detetion methods
FRR can detect the failure of a link timely and reroute traffic to the bypass LSP. It detects the status of
a link in one of the following three methods:
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Link layer protocol status detection: In this method, the interface type determines how fast the
FRR can detect a link failure.
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Cooperation of RSVP-TE and BFD: BFD is a fast detection mechanism, which can detect faults of
links or nodes timely. In this method, FRR can obtain the link status timely through BFD, so as to
implement fast switchover of links.
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RSVP hello: In this method, RSVP hello is enabled on each protected node and its neighbor
nodes along the primary LSP, so that a device periodically sends hello messages to its peer
device on the LSP. If a link or node fails, hello messages will be lost. If a device cannot receive
hello messages from its peer in three hello intervals, the hello mechanism concludes that a link
failure occurs. Hence, the hello mechanism is slower in link failure detection, compared with the
other two methods.