Configuration of S-BFD on SR-TE LSPs

For PCC-initiated or PCC-controlled LSPs, an operator can configure an S-BFD session under the bfd context of SR-TE LSP, the primary path, the SR-TE secondary path, and the lsp-template by using:

Classic CLI commands

config>router>mpls>lsp bfd

config>router>mpls >lsp>primary bfd

config>router>mpls>lsp>secondary bfd

config>router>mpls>lsp-template bfd
MD-CLI commands

configure router mpls lsp bfd

configure router mpls lsp primary bfd

configure router mpls lsp secondary bfd

configure router mpls lsp-template bfd

The operator can configure S-BFD to operate in one of the following modes:

routed return path

In this mode, the session initiator sends BFD packets on the LSP toward the reflector node. The reflector node sends the BFD reply packet back to the initiator through a routed return path. The remote discriminator value is determined by passing the ‟to” address of the LSP to BFD, which then matches it to a mapping table of peer IP addresses to reflector remote discriminators that are created by the centralized configuration under the IGP. If no match for the ‟to” address of the LSP exists, a BFD session is not established on the LSP or path. For more information, see the 7450 ESS, 7750 SR, 7950 XRS, and VSR OAM and Diagnostics Guide.

Note: A remote peer IP address to discriminator mapping must exist before bringing an LSP administratively up.
controlled return path

In this mode, operators configure a return path label for the BFD session to the initiator. The router pushes an additional MPLS label on S-BFD packets at the bottom of the stack and the BFD session operates in echo mode. The return path label refers to an MPLS binding SID of an SR policy programmed at the far end of the SR-TE LSP. The operator can use this SR policy to forward S-BFD reply packets along an explicit TE path back to the initiator, avoiding the IGP shortest path. The operator can configure different LSPs or LSP paths using different return path labels referring to different SR policies at the LSP far end. The SR policies can have segment lists with different paths, ensuring the BFD reply packets from different LSP paths do not share the same outcome. S-BFD packets on these sessions bypass the reflector at the far end of the LSP. Therefore, the operator does not need to configure a reflector discriminator for these sessions.

The referenced BFD template must specify parameters consistent with an S-BFD session. For example, the endpoint type is cpm-np for platforms supporting a CPM P-chip; otherwise, a CLI error is generated. Operators can use the same BFD template for both S-BFD and any other type of BFD session requested by MPLS.

If S-BFD is configured at the LSP level, sessions are created on all paths of the LSP.

Classic CLI commands

config>router>mpls
   lsp-template name on-demand-p2p-srte template-id
      bfd
        bfd-enable
        bfd-template name
        return-path-label label value
        wait-for-up-timer seconds

MD-CLI commands

*[gl:/configure router "Base" mpls lsp-template name]
                  type p2p-sr-te-on-demand
                  bfd              
                      bfd-liveness {true|false}
                      bfd-template reference
                      return-path-label number
                      wait-for-up-timer number

Operators can also configure S-BFD on the primary or a specific secondary path of the LSP, as follows:

Classic CLI commands

config>router>mpls>lsp name sr-te
   primary name
      bfd
        bfd-enable
        bfd-template name
        return-path-label label
        wait-for-up-timer seconds
        exit

config>router>mpls>lsp name sr-te
   secondary name
      bfd
        bfd-enable
        bfd-template name
        return-path-label label
        wait-for-up-timer seconds
        exit

MD-CLI commands

*[gl:/configure router "Base" mpls lsp name primary name]
                bfd
                  bfd-liveness {true|false}
                  bfd-template reference
                  return-path-label number
                  wait-for-up-timer number
                  exit

*[gl:/configure router "Base" mpls lsp name secondary name]
                bfd
                  bfd-liveness {true|false}
                  bfd-template reference
                  return-path-label number
                  wait-for-up-timer number
                  exit

The wait-for-up-timer is only applicable if a failure action is configured using the failover-or-down command. For more information, see Support for BFD failure action with SR-TE LSPs.

For PCE-initiated LSPs and SR-TE auto-LSPs, the operator specifies the S-BFD session parameters in the LSP template. The ‟to” address used for determining the remote discriminator is derived from the far-end address of the auto-LSP or PCE-initiated LSP.

Classic CLI commands

config>router>mpls
   lsp-template name mesh-p2p-srte 
      bfd
        bfd-enable
        bfd-template name
        wait-for-up-timer seconds

config>router>mpls
   lsp-template name one-hop-p2p-srte 
      bfd
        bfd-enable
        bfd-template
        wait-for-up-timer seconds

config>router>mpls
   lsp-template name on-demand-p2p-srte 
      bfd
        bfd-enable
        bfd-template name
        wait-for-up-timer seconds

MD-CLI commands

*[gl:/configure router "Base" mpls lsp-template name]
                  type p2p-sr-te-mesh
                  bfd
                    bfd-liveness {true|false}
                    bfd-template reference
                    wait-for-up-timer number

*[gl:/configure router "Base" mpls lsp-template name]
                  type p2p-sr-te-one-hop
                  bfd
                    bfd-liveness {true|false}
                    bfd-template reference
                    wait-for-up-timer number

*[gl:/configure router "Base" mpls lsp-template name]
                  type p2p-sr-te-on-demand
                  bfd
                    bfd-liveness {true|false}
                    bfd-template reference
                    wait-for-up-timer number