Configuring BFD for SR-MPLS BE (SR and LDP Interworking Scenario)

This section describes how to use BFD to detect an LSP fault in an SR+LDP interworking scenario.

Usage Scenario

SR and LDP interworking enables SR and LDP to work together on the same network. SR-MPLS BE and LDP networks can be connected through this technology to implement MPLS forwarding.

If BFD for SR-MPLS BE detects a fault on the primary tunnel when SR communicates with LDP, an application, such as VPN FRR, rapidly switches traffic to minimize the impact on traffic.

Pre-configuration Tasks

Before configuring BFD for SR-MPLS BE (in the SR and LDP interworking scenario), complete the following tasks:

Configure IS-IS SR to communicate with LDP or OSPF SR to communicate with LDP.
Set each LSR ID using the mpls lsr-id lsr-id command. Ensure that the route to the local lsr-id is reachable.

Procedure

Create a BFD session on the SR side.
1. Run system-view
  The system view is displayed.
2. Run bfd
  The BFD view is displayed.
3. Run mpls-passive
  The egress is enabled to create a BFD session passively.
  
  The egress has to receive an LSP ping request carrying a BFD TLV before creating a BFD session.
4. Run quit
  Return to the system view.
5. Run segment-routing
  The Segment Routing view is displayed.
6. Run bfd enable mode tunnel [ filter-policy ip-prefix ip-prefix-name | effect-sr-lsp | nil-fec ] ^*
  BFD is enabled for SR LSPs.
  
  If effect-sr-lsp is specified and BFD goes down, the SR LSPs are withdrawn.
  
  In an SR and LDP interworking scenario, the ingress node cannot detect whether LDP LSPs are stitched to SR LSPs in the LDP to SR direction. In the LSP ping packet triggered by BFD, the encapsulated FEC type is LDP. When the packet arrives at the egress node (SR node), the FEC type fails to be verified, preventing BFD from going Up. To resolve this issue, configure the nil-fec parameter.
7. (Optional) Run bfd tunnel { min-rx-interval receive-interval | min-tx-interval transmit-interval | detect-multiplier multiplier-value } ^*
  BFD parameters are set for SR tunnels.
8. Run commit
  The configuration is committed.
Create a BFD session on the LDP side.
1. Run system-view
  The system view is displayed.
2. Run bfd
  The BFD view is displayed.
3. Run mpls-passive
  The egress is enabled to create a BFD session passively.
  
  The egress has to receive an LSP ping request carrying a BFD TLV before creating a BFD session.
4. Run quit
  Return to the system view.
5. Run mpls
  The MPLS view is displayed.
6. Run mpls bfd enable
  An MPLS device to dynamically establish a BFD session.
7. Run mpls bfd-trigger host
  Host IP routes are used as the policy for triggering LDP BFD sessions.
8. Run commit
  The configuration is committed.
Configure a device that connects the LDP area to the SR area.
1. Run system-view
  The system view is displayed.
2. Run mpls
  The MPLS view is displayed.
3. Run lsp-trigger segment-routing-interworking best-effort host
  The device is enabled to stitch SR LSPs to the proxy egress LSPs and transit LSPs that are established over non-local host routes with a 32-bit mask.
4. Run commit
  The configuration is committed.

Verifying the Configuration

After successfully configuring BFD for SR-MPLS BE, run the display segment-routing bfd tunnel session [ prefix ip-address { mask | mask-length } ] command to check information about the BFD session that monitors SR LSPs.