Configuring BFD to Detect Public Network Links

Context

After BFD for PW is configured, the fault on a PW can be rapidly detected and service flows on the PW can be rapidly switched to the secondary PW. In this scenario, BFD can be configured in the following two modes:

If there are a small number of service PWs, configure BFD for service PWs.
If there are multiple PWs, configure BFD for mPW and associate service PWs with the mPW. In this way, BFD monitors service PWs by detecting the mPW.

The BFD control packets are encapsulated in the PW control packets. Therefore, the control word function must be enabled on the PWs to be detected by BFD.

Perform the following operations on PEs at both ends of the primary PW.

Procedure

Configure BFD for service PWs or the mPW.
1. Run system-view
  The system view is displayed.
2. Run bfd
  BFD is enabled globally, and the global BFD view is displayed.
3. Run quit
  Return to the system view.
4. Run bfd cfg-name bind pw interface interface-type interface-number [ secondary ]
  A BFD configuration item is created.
  - The outbound interface (specified by interface interface-type interface-number) to which a BFD session is bound is an AC interface on which a PW is established. If an mPW is bound to a BFD session, the interface is the loopback interface where the mPW is configured.
  - If the PW to be detected is a secondary PW, you must specify secondary.
5. (Optional) Run wtr wtr-value
  The time before a BFD session recovers is set.
  
  By default, the value is 0, indicating that a BFD session recovers immediately.
  
  Running this command can prevent applications from continuous active/standby switchovers during the BFD session flapping.
6. Configure local and remote discriminators.
  - Run discriminator local discr-value
    
    A local discriminator is configured.
  - Run discriminator remote discr-value
    
    A remote discriminator is configured.
  The local discriminator of one end must be the same as the remote discriminator of the other end of a BFD session.
7. Run commit
  The configuration is committed.
  
  If the status of a PW is Down, the BFD session can be established but cannot go Up.
  - The local and remote discriminators cannot be changed once being configured. To modify the local and remote discriminators, run the undo bfd bfd-name command in the system view to delete BFD for PW configurations. After that, you can re-configure the local and remote discriminators.
  - After the PW is deleted, the related BFD sessions and configurations are deleted.
(Optional) Associate service PWs with the mPW.
1. Run system-view
  The system view is displayed.
2. Run interface interface-type interface-number [ .subinterface-number ]
  The AC interface view is displayed.
3. Run mpls l2vc [ secondary | bypass ] track admin-vc interface loopback interface-number
  Service PWs on the AC interface are associated with the mPW.