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Link Protection and Node Protection

Link protection helps to ensure that traffic going over a specific interface to a neighboring router or switch can continue to reach this router (switch) if that interface fails. When link protection is configured for an interface and an LSP that traverses this interface, a bypass LSP is created that will handle this traffic if the interface fails. The bypass LSP uses a different interface and path to reach the same destination. The path used can be configured explicitly, or you can rely on CSPF. The RSVP metric for the bypass LSP is set in the range of 20,000 through 29,999 (this value is not user configurable).

If a link-protected interface fails, traffic is quickly switched to the bypass LSP. Note that a bypass LSP cannot share the same egress interface with the LSPs it monitors.

In Figure 1, link protection is enabled on Interface B between Router 1 and Router 2. It is also enabled on LSP A, an LSP that traverses the link between Router 1 and Router 2. If the link between Router 1 and Router 2 fails, traffic from LSP A is quickly switched to the bypass LSP generated by link protection.

Although LSPs traversing an interface can be configured to take advantage of link protection, it is important to note that it is specifically the interface that benefits from link protection. If link protection is enabled on an interface but not on a particular LSP traversing that interface, then if the interface fails, that LSP will also fail.


Link protection does not work on unnumbered interfaces.