Cisco Crosswork Planning Design 7.2.x User Guide

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Cisco Crosswork Planning Design 7.2.x User Guide

SR-TE protection

Updated: August 14, 2026

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Provides information on the attributes of SR-TE protection mechanism, including how they maintain network reliability and ensure traffic continuity.

If the network contains a configurable topology-independent loop-free alternate (TI-LFA), you can simulate SR-TE tunnels before and after convergence.
To see the simulation before convergence, you must be in Fast reroute mode (click or Actions > Edit > Network options and choose Fast reroute in the Simulation convergence mode section).

In the IGP and LSP Reconvergence mode, you can only see the after-convergence routes.

SR-TE tunnel simulation before convergence

In a normal path state, Cisco Crosswork Planning determines the no-failure route from segment list hop to segment list hop. Between segment list hops, Cisco Crosswork Planning follows the IGP shortest path to the next segment list hop. At each interface along the path, if the connected circuit is down, Cisco Crosswork Planning determines whether the next segment list hop is an interface or a node, and whether the SR tunnel is routable.

For each SR tunnel in a network model, and for each SID in the path, Cisco Crosswork Planning determines the no-failure route.

  • If SR FRR is enabled for the interface in the Interfaces table, Cisco Crosswork Planning configures the protect path state:

    • Cisco Crosswork Planning derives the post-convergence path from the local node to the next SID hop with the subject circuit removed from the topology.

    • The next SID hop depends on the SID hop type. For an interface SID, the next hop is the remote node of that interface. For a node SID, the next hop is that node.

    • Cisco Crosswork Planning follows the derived after-convergence path hop by hop until it reaches the next SID hop. (If a failure occurs along the way, the SR FRR and the SR LSP do not route.)

    • When Cisco Crosswork Planning reaches the next SID hop, it returns to the normal path state and resumes following the no-fail path to the SID hop.

  • If SR FRR is not enabled for the interface in the Interfaces table, the SR tunnel does not route.

Simulate SR-TE tunnels after convergence

Cisco Crosswork Planning routes to each segment list hop through the IGP shortest path under all failure conditions.

Note
An SR LSP might be routable before convergence through a TI-LFA, but unroutable after convergence.

Constraints for SR FRR and TI-LFA

These constraints define the behavior of protection features and path calculations.

  • In the Interfaces table, if the SR FRR enabled column displays "true" for a given interface, all SR LSPs with a node or interface SID as the next hop are protected over that interface. If the SRR FRR enabled column displays "false", all SR LSP SIDs are unprotected over that interface.

  • Protected versus unprotected adjacency SIDs are not supported. All adjacency SIDs are considered protected.

  • Cisco Crosswork Planning does not impose a limit on the TI-LFA path’s label stack depth.

  • Cisco Crosswork Planning does not explicitly derive P and Q nodes, but instead derives a protect path that aligns with the after-convergence shortest path from the PLR to the next segment list hop.

  • If any part of the TI-LFA path encounters a failure before reaching the next segment list hop, the TI-LFA path fails and the SR LSP does not route.