3Com S7906E Configuration Manual page 1661

Protection
FRR provides link protection and node protection for an LSP as follows:
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 1-4, the primary LSP is Router A → Router B → Router C → Router D, and the bypass LSP
is Router B → Router F → Router C.
Figure 1-4 FRR link protection
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 1-5, 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 1-5 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:
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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