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.
- 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.
