[Configuration and Deployment Instructions] BFD Discriminator Conflict

Scenario

As shown in Figure 1-3, a static BFD session is configured to monitor the link between Router A and Router B.

Figure 1-3  Periodic BFD session flapping 

Configuration Requirements

When BFD is deployed on a network, discriminators must be uniformly planned to prevent discriminator conflict.

Misconfiguration Risks

Risk description:

1. A static BFD session is configured on Router B, which establishes a session with Router A. The discriminator local discr-value command is run in the BFD view to set the local discriminator to a.

2. A static BFD session is configured on Router C, and the discriminator remote discr-value command is run in the BFD view to also set the remote discriminator to a.

When the preceding conditions are met, the BFD session periodically flaps, causing services bound to the BFD session to flap.

The BFD session Down reasons on both devices are both neighbor Down.

Identification method:

1. Check the static BFD session configurations on both devices.

   # Run the display this command in the BFD session view on Router B. The value of discriminator local must match the remote discriminator on Router A.

   <HUAWEI> system-view

   [HUAWEI] bfd session a

   [HUAWEI-bfd-session-a] display this

   #

   bfd a bind peer-ip 10.1.1.2

    discriminator local 1  

    discriminator remote 2

    commit

   #

   return

   # Run the display this command in the BFD session view on Router A. The value of discriminator local must match the remote discriminator on Router B.

   <HUAWEI> system-view

   [HUAWEI] bfd session a

   [HUAWEI-bfd-session-a] display this

   #

   bfd a bind peer-ip 10.1.1.1

    discriminator local 2

    discriminator remote 1  

    commit

   #

   return

2. Check detailed information about the BFD session.

   # Run the display bfd session all verbose command in the user view to check detailed information about the BFD session on Router A. The BFD session enters the NeighborDown state.

   <HUAWEI> display bfd session all verbose 

   --------------------------------------------------------------------------------

     (Multi Hop) State : Down                  Name : a

   --------------------------------------------------------------------------------

     Local Discriminator    : 1                Remote Discriminator   : 2 

     Session Detect Mode    : Asynchronous Mode Without Echo Function

     BFD Bind Type          : Peer IP Address  

     Active Multi           : -                  

     Last Local Diagnostic  : Neighbor Signaled Session Down

     ¡­¡­

   # Run the display bfd session all verbose command in the user view to check detailed information about the BFD session on Router B. The BFD session enters the NeighborDown state.

   <HUAWEI> display bfd session all verbose 

   --------------------------------------------------------------------------------

     (Multi Hop) State : Down                  Name : a

   --------------------------------------------------------------------------------

     Local Discriminator    : 2                Remote Discriminator   : 1 

     Session Detect Mode    : Asynchronous Mode Without Echo Function

     BFD Bind Type          : Peer IP Address  

     Active Multi           : -                  

     Last Local Diagnostic  : Neighbor Signaled Session Down

   ¡­¡­

3. Check the BFD session configuration on Router C.

   # Run the display current-configuration configuration bfd-session command in the user view to check whether any BFD session with local discriminator conflict exists on Router C. The value of discriminator remote conflicts with the remote discriminator on Router B.

   <HUAWEI> display current-configuration configuration bfd-session 

   #

   bfd a bind peer-ip 20.1.1.1

    discriminator local 5

    discriminator remote 1  

    commit

   #

   return

Recovery measures:

Change the remote discriminator of the BFD session on Router C to a different value.