Configuring Static BFD to Detect an LDP LSP
Context
BFD is bound to only the ingress node of an LDP LSP.
One LSP is bound to only one BFD session.
The detection only supports the LDP LSP that is triggered to establish by the host route.
The forwarding modes on the forwarding path and reverse path can be different (for example, an IP packet is sent from the source to the destination through an LSP, and is sent from the destination to the source in IP forwarding mode), but the forwarding path and reverse path must be established over the same link. If they use different links, BFD cannot identify the faulty path when a fault is detected.
Static BFD for LDP LSPs fast detect faults on an LDP LSP. Static BFD for LDP LSPs can be flexibly deployed, but needs to be manually controlled.
Pre-configuration Tasks
Before configuring static BFD to detect an LDP LSP, complete the following task:
Configuring a local LDP session according to Configuring Basic Functions of MPLS LDP
Configuring BFD with Specific Parameters on the Ingress Node
Context
BFD parameters on the ingress node include the local and remote discriminators, intervals for sending and receiving BFD packets, and local BFD detection multiplier. The BFD parameters affect BFD session setup.
You can adjust the local detection time according to the network situation. On an unstable link, if a small detection time is used, a BFD session may flap. You can increase the detection time of the BFD session.
NOTE: Actual interval for the local device to send BFD packets = MAX { locally configured interval for sending BFD packets, remotely configured interval for receiving BFD packets }
Actual interval for the local device to receive BFD packets = MAX { remotely configured interval for sending BFD packets, locally configured interval for receiving BFD packets }
Local detection time = Actual interval for receiving BFD packets x Remotely configured BFD detection multiplier
Perform the following steps on the ingress node of an LSP:
Procedure
- Run system-view
The system view is displayed.
- Run bfd
This node is enabled with the global BFD function. The global BFD view is displayed.
By default, global BFD is disabled.
- Run quit
Return to the system view.
- Run bfd cfg-name bind ldp-lsp peer-ip ip-address nexthop ip-address [ interface interface-type interface-number ]
The BFD session is bound to a dynamic LSP.
When the IP address of the egress node on the LSP to be detected is borrowed or lent, an interface must be specified.
- Set local and remote discriminators of a BFD session.
Run discriminator local discr-value
The local discriminator is configured.
Run discriminator remote discr-value
The remote discriminator is configured.
NOTE:
The local and remote identifiers on both ends of a BFD session must be consistent with each other; otherwise, the session cannot be established correctly. In addition, the local and remote identifiers cannot be modified after configuration.
- (Optional) Run min-tx-interval interval
The interval for sending BFD packets is set on the local device.
By default, the interval for sending BFD packets is 1000 ms.
- (Optional) Run min-rx-interval interval
The interval for receiving BFD packets is set on the local device.
By default, the interval for receiving BFD packets is 1000 ms.
- (Optional) Run detect-multiplier multiplier
The local BFD detection multiplier is set.
The default value is 3.
- Run process-pst
The changes of BFD session status can be advertised to the application on the upper layer.
By default, a static BFD session cannot report faults of the monitored service module to the system.
- Run commit
The configuration is committed.
Configuring BFD with Specific Parameters on the Egress Node
Context
BFD parameters on the egress node includes the local and remote discriminators, intervals for sending and receiving BFD packets, and local BFD detection multiplier. The BFD parameters affect BFD session setup.
You can adjust the local detection time according to the network situation. On an unstable link, if a small detection time is used, a BFD session may flap. You can increase the detection time of the BFD session.
NOTE: Actual interval for the local device to send BFD packets = MAX {locally configured interval for sending BFD packets, remotely configured interval for receiving BFD packets}
Actual interval for the local device to receive BFD packets = MAX {remotely configured interval for sending BFD packets, locally configured interval for receiving BFD packets}
Local detection time = Actual interval for receiving BFD packets x Remotely configured BFD detection multiplier
Perform the following steps on the egress node of the LSP.
Procedure
- Run system-view
The system view is displayed.
- Run bfd
This node is enabled with global BFD. The global BFD view is displayed.
By default, global BFD is disabled.
- Run quit
Return to the system view.
- 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 BFD packets are received and sent
along the same path, an LSP or TE tunnel is preferentially used to inform the egress node of an LSP fault. If the configured reverse tunnel requires BFD detection, configure a pair of BFD sessions for
it. Run the following commands as required.
For the IP link, run:
bfd cfg-name bind peer-ip peer-ip [ vpn-instance vpn-instance-name ] [ interface interface-type interface-number ] [ source-ip source-ip ]
For the dynamic LSP, run:
bfd cfg-name bind ldp-lsp peer-ip ip-address nexthop ip-address [ interface interface-type interface-number ]
For the static LSP, run:
bfd cfg-name bind static-lsp lsp-name
For MPLS TE, run:
bfd cfg-name bind mpls-te interface tunnel interface-number [ te-lsp [ backup ] ]
- Set local and remote discriminators of a BFD session.
Run discriminator local discr-value
The local discriminator is configured.
Run discriminator remote discr-value
The remote discriminator is configured.
NOTE:
The local identifier and remote identifier on both ends of a BFD session must accord with each other. The session cannot be established correctly otherwise. In addition, the local identifier and remote identifier cannot be modified after configuration.
- (Optional) Run min-tx-interval interval
The interval for sending BFD packets is set on the local device.
By default, the interval for sending BFD packets is 1000 ms.
- (Optional) Run min-rx-interval interval
The interval for receiving BFD packets is set on the local device.
By default, the interval for receiving BFD packets is 1000 ms.
- (Optional) Run detect-multiplier multiplier
The local BFD detection multiplier is set.
The default value is 3.
- (Optional) Run process-pst
The changes of the BFD session status can be advertised to the upper-layer application.
By default, a static BFD session cannot report faults of the monitored service module to the system.
If an LSP is used as a reverse tunnel to notify the ingress 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.
- Run commit
The configuration is committed.