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[Configuration and Deployment Instructions] BFD Detection Interval of the Inner-Layer Link Is Greater than That of the Outer-Layer Link

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BFD Detection Interval of the Inner-Layer Link Is Greater than That of the Outer-Layer Link

In a multi-layer protection scenario, if the BFD detection interval of the inner-layer link is greater than that of the outer-layer link, inner-layer protection switching has not been triggered when BFD detects a fault on the outer-layer link.

Scenario

Multi-layer protection is configured. For example, BFD for RSVP, BFD for CR-LSP, or BFD for TE is configured.

Configuration Requirements

When BFD is deployed on a network and multi-layer protection is configured, the BFD detection interval of the inner-layer link must be less than that of the outer-layer link.

Different BFD detection intervals are configured in different scenarios. For example:
  • For BFD for RSVP scenarios, see (Optional) Adjusting BFD Parameters.
  • For static BFD for CR-LSP scenarios, see Configuring BFD Parameters on the Ingress of the Tunnel and Configuring BFD Parameters on the Egress of the Tunnel.
  • For dynamic BFD for CR-LSP scenarios, see (Optional) Adjusting BFD Parameters.
  • For BFD for TE scenarios, see Configuring BFD Parameters on the Ingress of the Tunnel and Configuring BFD Parameters on the Egress of the Tunnel.

Misconfiguration Risks

Risk description:

In a multi-layer protection scenario, the BFD detection interval of the inner-layer link is greater than that of the outer-layer link. If the tunnel fails, the BFD session detecting the outer-layer link first detects the fault due to a small detection interval. The BFD session then triggers protection switching for tunnel services, which wastes inner-layer protection switching.

In this situation, only outer-layer protection switching is used, which deteriorates overall switching performance.

Identification method:

The following identification method applies when dynamic BFD for CR-LSP is configured to detect the inner-layer link, static BFD for TE is configured to detect the outer-layer link, and BFD for TE and BFD for CR-LSP are bound to the same tunnel interface. Identify the risk in other scenarios according to the actual situation.

Run the display bfd session all verbose command in the user view to check BFD detection intervals.

As shown in the command output, the detection interval of the BFD session detecting the inner-layer link (BFD Bind Type is TE_LSP) is 2664 ms, whereas the detection interval of the BFD session detecting the outer-layer link (BFD Bind Type is TE_TUNNEL) is 300 ms. That is, the BFD detection interval of the inner-layer link is greater than that of the outer-layer link.

<HUAWEI> display bfd session all verbose
--------------------------------------------------------------------------------
  State : Up                    Name : dyn_16393
--------------------------------------------------------------------------------
  Local Discriminator    : 16393            Remote Discriminator   : 16402 
  Session Detect Mode    : Asynchronous Mode Without Echo Function  BFD Bind Type          : TE_LSP 
  Bind Session Type      : Dynamic  
  Bind Peer IP Address   : 2.2.2.2         
  NextHop Ip Address     : 10.1.1.2 
  Bind Interface         : Tunnel1          TE LSP Type            : Primary 
  Tunnel ID              : 33  
  FSM Board Id           : 9                TOS-EXP                : 6
  Min Tx Interval (ms)   : 999              Min Rx Interval (ms)   : 888 
  Actual Tx Interval (ms): 999              Actual Rx Interval (ms): 888 
  Local Detect Multi     : 48               Detect Interval (ms)   : 2664 
  Echo Passive           : Disable          Acl Number             : - 
  Destination Port       : 3784             TTL                    : 1 
  Proc Interface Status  : Disable          Process PST            : Enable     
  WTR Interval (ms)      : -                Config PST             : Enable     
  Active Multi           : 3   
  Last Local Diagnostic  : No Diagnostic
  Bind Application       : TE
  Session TX TmrID       : -                Session Detect TmrID   : - 
  Session Init TmrID     : -                Session WTR TmrID      : - 
  Session Echo Tx TmrID  : -   
  Session Description    : - 
--------------------------------------------------------------------------------

--------------------------------------------------------------------------------
  State : Up                    Name : te
--------------------------------------------------------------------------------
  Local Discriminator    : 111              Remote Discriminator   : 111 
  Session Detect Mode    : Asynchronous Mode Without Echo Function  BFD Bind Type          : TE_TUNNEL 
  Bind Session Type      : Static  
  Bind Peer IP Address   : 2.2.2.2         
  NextHop Ip Address     : -.-.-.-  
  Bind Interface         : Tunnel1                                           
  Tunnel ID              : 33  
  FSM Board Id           : 9                TOS-EXP                : 1
  Min Tx Interval (ms)   : 100              Min Rx Interval (ms)   : 100 
  Actual Tx Interval (ms): 100              Actual Rx Interval (ms): 100 
  Local Detect Multi     : 3                Detect Interval (ms)   : 300 
  Echo Passive           : Disable          Acl Number             : - 
  Destination Port       : 3784             TTL                    : 1 
  Proc Interface Status  : Disable          Process PST            : Disable    
  WTR Interval (ms)      : -                Config PST             : Disable    
  Active Multi           : 3   
  Last Local Diagnostic  : No Diagnostic
  Bind Application       : No Application Bind
  Session TX TmrID       : -                Session Detect TmrID   : - 
  Session Init TmrID     : -                Session WTR TmrID      : - 
  Session Echo Tx TmrID  : -   
  Session Description    : - 
--------------------------------------------------------------------------------

Total UP/DOWN Session Number : 2/0

Recovery measures:

Change the BFD detection interval of the inner-layer link to a value less than that of the outer-layer link.


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