BFD for Static Routes

A static route is associated with a static BFD when the next-hop for the static route matches the neighbor address of the static BFD neighbor and BFD monitoring is enabled for the static route.

To use BFD for static routes, configure static routes (IPv4 or IPv6) and the corresponding static BFD separately. When static BFD is configured, the static route manager checks the routing table (RIBMGR) for a route to the BFD neighbor.

If a route exists and the next-hop is directly connected, a single-hop session is created.
If the next-hop is not directly connected, a multi-hop BFD session is created.

When the BFD session is up, a corresponding static route is added to RIBMGR. When the BFD session that monitors the static route goes down because the BFD neighbor is not reachable, static routes are removed from RIBMGR. These removed routes are replaced in RIBMGR when the BFD neighbor is reachable.

Single-hop BFD sessions use timeout values that are configured on the outgoing interface from which the BFD neighbor is reachable. Timeout values for multi-hop BFD sessions are specified with the static BFD neighbor. Multiple static routes with the same BFD neighbor use the same BFD session and timeout values.

Considerations for BFD for static routes

When you configure a static BFD for a neighbor and the neighbor is reachable, a request is made to BFD to establish a BFD session.
A single-hop BFD static route session uses the timer values that are configured for the outgoing interface to the directly connected neighbors. A multi-hop BFD static route session uses the timer values that are configured in the CLI. If these timer values conflict with the timer values set for BGP, for the same next-hop, then BFD uses the smaller value to meet the more stringent requirement.
After a reboot of the device, global config-replay happens before interface config-replay. In such a situation, static BFD sessions can be created before static routes are added to RIBMGR. Therefore, for SLX-OS, BFD sessions are created only when the next-hop is reachable.
If you remove the static BFD session, BFD takes down the corresponding session without removing static routes from routing table. Ongoing traffic is not interrupted.
If a BFD session goes down because the BFD neighbor is not reachable, the associated static routes are removed from RIBMGR. Traffic is interrupted on these static routes.
If the maximum number of BFD sessions is reached, a BFD session may not come up. In such a situation, a BFD session is not created for the related static route and the route is not removed from RIBMGR.

BFD for IPv6 static routes

If the BFD neighbor is link-local, the source IPv6 address must also be link-local.

If an IPv6 BFD session is running for a link-local BFD neighbor, the interface-type and interface-name parameters (for the ipv6 route static bfd command) are mandatory because the link-local address can be the same on multiple interfaces.

Supported Platforms

BFD for static routes is supported on SLX 9150 and SLX 9250.