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. For more information, see ‟Seamless Bidirectional Forwarding Detection (S-BFD)” in 7450 ESS, 7750 SR, 7950 XRS, and VSR OAM and Diagnostics Guide. S-BFD also requires centralized configuration for the 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 user guide describes the application of S-BFD to SR-TE LSPs, and the LSP configuration required for this feature.
By default, S-BFD operates in asynchronous mode. The reflector encapsulates and routes IP/UDP encapsulated S-BFD packets back to the initiator using the IGP shortest path. SR OS also supports a controlled return TE path for BFD reply packets when S-BFD operates in echo mode with the reflector router forwarding packets back toward the initiator on a specified labelled path using, for example, an SR policy. This allows the operator to configure a specific TE return path for each S-BFD session on an SR-TE LSP at the initiating node. In this case, the reflector function at the tail end of the LSP is bypassed.
S-BFD is supported in the following SR objects or contexts:
PCC-Initiated:
SR-TE LSP level
SR-TE primary path
SR-TE secondary and standby path
PCE-Initiated SR-TE LSPs
SR-TE auto-LSPs