BFD static routing

Bidirectional Forwarding Detection (BFD) provides short-duration detection of failures in the path between adjacent forwarding devices. You can now associate BFD with static routes to monitor the reachability of the next-hop gateway. When BFD is configured over a static route, it monitors the connectivity of the local router with the next hop IP. BFD must be configured on the local router interface as well as the next-hop router interface.

If a failure occurs, the corresponding BFD session is taken down and the corresponding static route entry from the Routing Information Base (RIB) is removed. If an alternate route to the destination exists, it is automatically added to the RIB. When the BFD session goes down, the session is not deleted, but the reachability of the next hop is attempted periodically by sending periodic BFD control packets. Once the next hop is reachable, BFD changes the session state to UP and installs the corresponding route in the RIB.

If the static route already exits, BFD can be configured on top of it. Nothing changes. If the static route does not exist, it can be configured along with the BFD configuration.

The ip route bfd command helps to enable BFD under ip static route for a particular next-hop destination and BFD source IP.

When BFD is configured over a static route, BFD starts monitoring the connectivity of the local router with the next hop ip. Static routes are added to or removed from the Routing Information Base (RIB) based on the status of BFD sessions. To successfully establish a BFD session, BFD should be configured on the local router interface as well as the next-hop router interface. BFD starts monitoring a given static route once the corresponding BFD session reaches the UP state.

Connectivity to the next hop router may be lost due to an event like an interface down or a neighbor going down; in such a scenario, BFD can detect such failures and trigger corrective measures to reduce network outages. When BFD detects a link failure (that is, BFD does not receive a control or echo packet for a specified amount of time), it takes the corresponding BFD session down and removes the corresponding static route entry from the RIB. If an alternate route to destination exists, it is automatically added to the RIB.

When the BFD session goes down, the session is not deleted. Once the next hop is reachable, BFD changes the session state to UP and installs the corresponding route in the RIB.

The BFD session is maintained in the BFD session database until it is explicitly removed by the user. Static route BFD is not supported for monitoring multi-hop connectivity.