Routing

Answer

Fast reroute provides a mechanism for automatically rerouting traffic on an LSP if a node or link in an LSP fails, thus reducing the loss of packets traveling over the LSP. For point-to-multipoint LSPs with fast reroute, only link protection is supported; node protection is not supported.

Supported functionality for link protection on point-to-multipoint includes:

• Link protection can be provided for all constituent sub-LSPs of a point-to-multipoint LSP in the event of a link failure.
• The protection LSP is a point-to-multipoint bypass LSP, set up using existing point-to-point bypass LSP (facility backup) mechanisms. The path of the bypass point-to-point LSP can be determined using Constrained Shortest Path First (CSPF) or it can be configured.

Not supported functionality for link protection on point-to-multipoint includes:

• Global repair is not supported: If a link fails and local repair is performed using link protection, the ingress does not attempt to perform global repair. Because there is no secondary LSP or CSPF, traffic remains on the bypass LSP until the link comes back up.
• Regular fast reroute one-to-one detours are not supported because node protection is not supported; instead, link protection is provided by using bypass LSPs.

For more information, click Layer 3 VPNs Feature Guide.