Verifying Next Hops For Static Routes; How Bfd Next-Hop Verification Works - Juniper IGP - CONFIGURATION GUIDE V11.1.X Configuration Manual

NOTE: A dynamically learned route can also resolve indirect next hops, as long as
the administrative distance value of the learned route is better (lower) than the static
route whose next hop is being resolved.

Verifying Next Hops for Static Routes

You can configure either Bidirectional Forwarding Detection (BFD) or Response Time
Reporter (RTR) probes to further control when a static route is installed in the routing
table. Using either BFD or RTR, static route installation is based on two factors:
whether the next hop to the specified destination is resolved, and whether an IP
service running above the static route application is currently available.
Next-hop verification is useful for static route configurations in which the layer 2 and
layer 3 interfaces are up and the next hop to the specified destination is available,
but the IP services that run above the static route are currently unavailable. When
the upper-layer IP services are unavailable, the router does not install the static route
in its routing table.

How BFD Next-Hop Verification Works

Static routes on E Series routers can use Bidirectional Forwarding Detection (BFD)
to verify the availability of the next hop and obtain the state of the IP service. For
additional information about BFD, see JUNOSe IP Services Configuration Guide.
If you specify the bfd-liveness-detection keywords with a minimum receive interval,
minimum transmit interval, or multiplier when you issue the ip route command to
establish a static route, the router verifies the next-hop status and installs the static
route in the routing table under the following conditions:
NOTE: BFD next-hop verification does not currently function in a multi-hop
configuration.
You can further control the installation of static routes by specifying the last-resort
keyword, which is valid when you use the bfd-liveness-detection keywords in the
ip route command. The last-resort keyword instructs the router to install the static
route in the routing table even if the specified BFD operation is unreachable, provided
that no other static route to the same network prefix is available.
The static route is removed from the routing table if the next hop is no longer
reachable and reinstalled when the route becomes reachable again.
You configure the static routes with the actual next hop address and not just
interface details.
The BFD protocol is operational on both ends of the verification.
The next hop is adjacent to the router (that is, only one hop away).
The next hop to the specified IP destination address is resolved.
Chapter 1: Configuring IP
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IP Routing