Configuring BFD Parameters on the Egress Node of the Tunnel

Procedure

1. Run system-view

   The system view is displayed.

2. Configure a reverse tunnel to inform the ingress node of a fault if the fault occurs. The reverse tunnel can be the IP link, LSP, or TE tunnel. To ensure that the forward and reverse paths are over the same link, a TE tunnel is preferentially selected to notify the ingress node of an LSP fault. Run the following commands as required.

   • For an IP link, run bfd session-name bind peer-ip ip-address [ vpn-instance vpn-name ] [ interface interface-type interface-number] [ source-ip ip-address ]

   • For an LDP LSP, run bfd session-name bind ldp-lsp peer-ip ip-address nexthop ip-address [ interface interface-type interface-number ]

   • For a static LSP, run bfd session-name bind static-lsp lsp-name

   • For a TE tunnel, run bfd session-name bind mpls-te interface tunnel interface-number

   

   When an IP link is used as the reverse tunnel, you do not need to perform steps 8 and 9.

3. Run discriminator local discr-value

   The local discriminator is set.

4. Run discriminator remote discr-value

   The remote discriminator is set.

5. (Optional) Run min-tx-interval interval

   The local interval at which BFD packets are sent is set.

6. (Optional) Run min-rx-interval interval

   The local interval at which BFD packets are received is set.

7. (Optional) Run detect-multiplier multiplier

   The local detection multiplier is adjusted.

   By default, the local detection multiplier is 3.

   Actual local sending interval = MAX { Configured local sending interval, Configured remote receiving interval }

   Actual local receiving interval = MAX { Configured remote sending interval, Configured local receiving interval }

   Actual local detection interval = Actual local receiving interval x Configured remote detection multiplier

   For example:

   • The local sending and receiving intervals are set to 200 ms and 300 ms respectively and the detection multiplier is set to 4.

   • The remote sending and receiving intervals are set to 100 ms and 600 ms respectively and the detection multiplier is set to 5.

   Then,

   • Actual local sending interval = MAX {200 ms, 600 ms} = 600 ms; Actual local receiving interval = MAX {100 ms, 300 ms} = 300 ms; Actual local detection interval is 300 ms x 5 = 1500 ms.

   • Actual remote sending interval = MAX {100 ms, 300 ms} = 300 ms; Actual remote receiving interval = MAX {200 ms, 600 ms} = 600 ms; Actual remote detection interval is 600 ms x 4 = 2400 ms.

8. (Optional) Run process-pst

   The system is enabled to modify the port status table (PST) when the BFD session status changes.

   If an LSP or a TE tunnel is used as a reverse tunnel to notify the ingress node of a fault, you can run this command to allow the reverse tunnel to switch traffic if the BFD session goes Down. If a single-hop IP link is used as a reverse tunnel, this command can be configured. Because the process-pst command can be only configured for BFD single-link detection.

9. Run notify neighbor-down

   A BFD session is configured to notify the upper layer protocol when the BFD session detects a neighbor Down event.

   In most cases, when you use a BFD session to detect link faults, the BFD session notifies the upper layer protocol of a link fault in the following scenarios:

   • When the BFD detection time expires, the BFD session notifies the upper layer protocol. BFD sessions must be configured on both ends. If the BFD session on the local end does not receive any BFD packets from the remote end within the detection time, the BFD session on the local end concludes that the link fails and notifies the upper layer protocol of the link fault.
   • When a BFD session detects a neighbor Down event, the BFD session notifies the upper layer protocol. If the BFD session on the local end detects a neighbor Down event within the detection time, the BFD session on the local end directly notifies the upper layer protocol of the neighbor Down event.

   When you use a BFD session to detect faults on an LSP, you need only be concerned about whether a fault occurs on the link from the local end to remote end. In this situation, run the notify neighbor-down command to configure the BFD session to notify the upper layer protocol only when the BFD session detects a neighbor Down event. This configuration prevents the BFD session from notifying the upper layer protocol when the BFD detection time expires and ensures that services are not interrupted.

10. Run commit

    The current configuration is committed.