This feature reuses of the capabilities of SR-TE LSPs to SR policy, so that operators wanting to use SR policies to enable more flexible and dynamic policy-based routing can benefit from network-based data path monitoring and fast protection switching.
Seamless BFD (S-BFD) is a form of BFD that requires significantly less state and reduces the need for session bootstrapping as compared to LSP BFD. See Seamless Bidirectional Forwarding Detection (S-BFD) in the 7450 ESS, 7750 SR, 7950 XRS, and VSR OAM and Diagnostics Guide. S-BFD requires centralized configuration of a reflector function, as well as a mapping at the head-end node between the remote session discriminator and the IP address for the reflector by each session. This configuration and the mapping are described in the 7450 ESS, 7750 SR, 7950 XRS, and VSR OAM and Diagnostics Guide.
This section describes the application of S-BFD to SR-Polices and the configuration required for this feature. See Seamless BFD for SR-TE LSPs for details of the application of S-BFD to SR-TE LSPs.
S-BFD provides a connectivity check for the data path of a segment list in an SR policy, and can determine whether the segment list is up. In addition, the router also supports two protection modes for an SR policy that are distinguished by the data path programming characteristics and whether uniform failover is required between segment lists in the same SR policy candidate path (ECMP protected mode), or between the programmed candidate paths (linear mode). These protection modes are driven by the S-BFD session state on the programmed segment lists of an SR policy.