Supported Platforms
Configuring BFD for MPLS IPv4 LSPs
You can configure Bidirectional Forwarding Detection (BFD) protocol on MPLS IPv4 LSPs as outlined in the Internet draft draft-ietf-bfd-mpls-02.txt, BFD for MPLS LSPs. BFD is used as a periodic Operation, Administration, and Maintenance (OAM) feature for LSPs to detect LSP data plane faults. You can configure BFD for LSPs that use either LDP or RSVP as the signaling protocol.
You can also use the LSP ping commands to detect LSP data plane faults. However, BFD has a couple of benefits: it requires less computer processing than LSP ping commands and can quickly detect faults in large numbers of LSPs (LSP ping commands must be issued for each LSP individually). On the other hand, BFD cannot be used to verify the control plane against the data plane at the egress LSR, which is possible when an LSP ping echo request is associated with a forwarding equivalence class (FEC).
The BFD failure detection timers are adaptive and can be adjusted to be more or less aggressive. For example, the timers can adapt to a higher value if the adjacency fails, or a neighbor can negotiate a higher value for a timer than the configured value. The timers adapt to a higher value when a BFD session flap occurs more than three times in a span of 15 seconds. A back-off algorithm increases the receive (Rx) interval by two if the local BFD instance is the reason for the session flap. The transmission (Tx) interval is increased by two if the remote BFD instance is the reason for the session flap. You can use the clear bfd adaptation command to return BFD interval timers to their configured values. The clear bfd adaptation command is hitless, meaning that the command does not affect traffic flow on the routing device.
For configuration instructions for LDP-signaled LSPs, see Configuring BFD for LDP LSPs. For configuration instructions for RSVP-signaled LSPs, see the following section.
Configuring BFD for RSVP-Signaled LSPs
BFD for RSVP supports unicast IPv4 LSPs. When BFD is configured for an RSVP LSP on the ingress router, it is enabled on the primary path and on all standby secondary paths for that LSP. You can enable BFD for all LSPs on a router or for specific LSPs. If you configure BFD for a specific LSP, whatever values configured globally for BFD are overridden. The BFD sessions originate only at the ingress router and terminate at the egress router.
An error is logged whenever a BFD session for a path fails. The following example shows how BFD for RSVP LSP log messages might appear:
RPD_MPLS_PATH_BFD_UP: MPLS BFD session for path path1 up on LSP R0_to_R3 RPD_MPLS_PATH_BFD_DOWN: MPLS BFD session for path path1 down on LSP R0_to_R3
You can configure BFD for all of the RSVP LSPs on the router, a specific LSP, or the primary path of a specific LSP. To configure BFD for RSVP LSPs, include the oam and bfd-liveness-detection statements.
You can configure this statement at the following hierarchy levels:
- [edit protocols mpls]
- [edit protocols mpls label-switched-path lsp-name]
- [edit protocols mpls label-switched-path lsp-name primary path-name]
The bfd-liveness-detection statement includes the following options:
- minimum-interval—Specifies the minimum transmit and receive interval.
- minimum-receive-interval—Specifies the minimum receive interval. The range is from 1 through 255,000 milliseconds.
- minimum-transmit-interval—Specifies the minimum transmit interval. The range is from 1 through 255,000 milliseconds.
- multiplier—Specifies the detection time
multiplier. The range is from 1 through 255.
Note: To avoid triggering false negatives, configure a BFD fault detection time that is longer than the fast reroute time.
You can also configure the lsp-ping-interval option to adjust the time interval between LSP pings. The LSP ping command for RSVP-signaled LSPs is ping mpls rsvp. For more information on the ping mpls rsvp command, see the Junos OS Operational Mode Commands.
Configuring a Failure Action for the BFD Session on an RSVP LSP
When the BFD session for an RSVP LSP goes down, the LSP is torn down and resignaled. Traffic can be switched to a standby LSP, or you can simply tear down the LSP path. Any actions performed are logged.
When a BFD session for an RSVP LSP path goes down, you can configure the Junos OS to resignal the LSP path or to simply disable the LSP path. A standby LSP path could be configured to handle traffic while the primary LSP path is unavailable. The router can automatically recover from LSP failures that can be detected by BFD. By default, if a BFD session fails, the event is simply logged.
To enable the Junos OS to tear down an RSVP LSP path in the event of a BFD event, include the failure-action statement:
For a list of the hierarchy levels at which you can include this statement, see the statement summary section for this statement.
You can configure either the teardown or make-before-break options:
- teardown—Causes the LSP path to be taken down and resignaled immediately.
- make-before-break—Causes the Junos OS to attempt to signal a new LSP path before tearing down the old LSP path. You can also configure the teardown-timeout option to automatically tear down the LSP after the time period specified if the attempt to resignal the LSP fails within the teardown-timeout interval. If you specify a value of 0 for the teardown-timeout interval, the LSP is taken down and resignaled immediately (the same behavior as when you configure the teardown option).
To configure a failure action for all of the RSVP LSPs, include the failure-action statement at the [edit protocols mpls oam bfd-liveness-detection] hierarchy level. To configure a failure action for a specific RSVP LSP, include the failure-action statement at the [edit protocols mpls label-switched-path lsp-name oam bfd-liveness-detection] hierarchy level.
To configure a failure action for a specific primary path, include the failure-action statement at the [edit protocols mpls label-switched path lsp-name primary path-name oam bfd-liveness-detection] hierarchy level. To configure a failure action for a specific secondary LSP path, include the failure-action statement at the [edit protocols mpls label-switched-path lsp-name secondary path-name oam bfd-liveness-detection] hierarchy level.
