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Configuring Adaptive LSPs

 

An LSP occasionally might need to reroute itself for these reasons:

  • The continuous reoptimization process is configured with the optimize-timer statement.

  • The current path has connectivity problems.

  • The LSP is preempted by another LSP configured with the priority statement and is forced to reroute.

  • The explicit-path information for an active LSP is modified, or the LSP’s bandwidth is increased.

You can configure an LSP to be adaptive when it is attempting to reroute itself. When it is adaptive, the LSP holds onto existing resources until the new path is successfully established and traffic has been cut over to the new LSP. To retain its resources, an adaptive LSP does the following:

  • Maintains existing paths and allocated bandwidths—This ensures that the existing path is not torn down prematurely and allows the current traffic to continue flowing while the new path is being set up.

  • Avoids double-counting for links that share the new and old paths—Double-counting occurs when an intermediate router does not recognize that the new and old paths belong to the same LSP and counts them as two separate LSPs, requiring separate bandwidth allocations. If some links are close to saturation, double-counting might cause the setup of the new path to fail.

By default, adaptive behavior is disabled. You can include the adaptive statement in two different hierarchy levels.

If you specify the adaptive statement at the LSP hierarchy levels, the adaptive behavior is enabled on all primary/secondary paths of the LSP. This means both the primary and secondary paths share the same bandwidth on common links.

To configure adaptive behavior for all LSP paths, include the adaptive statement in the LSP configuration:

You can include this statement at the following hierarchy levels:

If you specify the adaptive statement at the [edit protocols mpls label-switched-path lsp-name (primary | secondary) path-name] hierarchy level, adaptive behavior is enabled only on the path on which it is specified. Bandwidth double-counting occurs between different paths. However, if you also have the adaptive statement configured at the [edit protocols mpls label-switched-path lsp-name] hierarchy level, it overrides the adaptive behavior of each individual path.

To configure adaptive behavior for either the primary or secondary level, include the adaptive statement:

You can include this statement at the following hierarchy levels: