Supported Platforms
Configuring BFD for LDP LSPs
You can configure Bidirectional Forwarding Detection (BFD) for LDP LSPs. The BFD protocol is a simple hello mechanism that detects failures in a network. Hello packets are sent at a specified, regular interval. A neighbor failure is detected when the router or switch stops receiving a reply after a specified interval. BFD works with a wide variety of network environments and topologies. The failure detection timers for BFD have shorter time limits than the failure detection mechanisms of static routes, providing faster detection.
An error is logged whenever a BFD session for a path fails. The following shows how BFD for LDP LSP log messages might appear:
RPD_LDP_BFD_UP: LDP BFD session for FEC 10.255.16.14/32 is up RPD_LDP_BFD_DOWN: LDP BFD session for FEC 10.255.16.14/32 is down
You can also configure BFD for RSVP LSPs, as described in Configuring BFD for MPLS IPv4 LSPs.
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.
To enable BFD for LDP LSPs, include the oam and bfd-liveness-detection statements:
You can enable BFD for the LDP LSPs associated with a specific forwarding equivalence class (FEC) by configuring the FEC address using the fec option at the [edit protocols ldp] hierarchy level. Alternatively, you can configure an Operation Administration and Management (OAM) ingress policy to enable BFD on a range of FEC addresses. For more information, see Configuring OAM Ingress Policies for LDP.
You cannot enable BFD LDP LSPs unless their equivalent FEC addresses are explicitly configured or OAM is enabled on the FECs using an OAM ingress policy. If BFD is not enabled for any FEC addresses, the BFD session will not come up.
You can configure the oam statement at the following hierarchy levels:
- [edit protocols ldp]
- [edit logical-systems logical-system-name protocols ldp]
The oam statement includes the following options:
- fec—Specify the FEC address. You must either specify a FEC address or configure an OAM ingress policy to ensure that the BFD session comes up.
- lsp-ping-interval—Specify the duration of the LSP ping interval in seconds. To issue a ping on an LDP-signaled LSP, use the ping mpls ldp command. For more information, see the Junos OS Operational Mode Commands.
The bfd-liveness-detection statement includes the following options:
- ecmp—Cause LDP to establish BFD sessions for all ECMP paths configured for the specified FEC. If you configure the ecmp option, you must also configure the periodic-traceroute statement for the specified FEC. If you do not do so, the commit operation fails. You can configure the periodic-traceroute statement at the global hierarchy level ([edit protocols ldp oam]) while only configuring the ecmp option for a specific FEC ([edit protocols ldp oam fec address bfd-liveness-detection]).
- holddown-interval—Specify the duration the BFD session should remain up before adding the route or next hop. Specifying a time of 0 seconds causes the route or next hop to be added as soon as the BFD session comes back up.
- minimum-interval—Specify the minimum transmit and receive interval. If you configure the minimum-interval option, you do not need to configure the minimum-receive-interval option or the minimum-transmit-interval option.
- minimum-receive-interval—Specify the minimum receive interval. The range is from 1 through 255,000 milliseconds.
- minimum-transmit-interval—Specify the minimum transmit interval. The range is from 1 through 255,000 milliseconds.
- multiplier—Specify the detection time multiplier. The range is from 1 through 255.
