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:

• 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).

  Note: BFD next-hop verification does not currently function in a multi-hop configuration.

• The next hop to the specified IP destination address is resolved.

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.

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