BFD Support for OSPF
BFD support for OSPFv2 and OSPFv3 can be configured so that OSPF is a registered protocol
with BFD. When BFD support for OSPF is configured, forwarding path detection failure
messages are received from BFD. BFD sessions can rapidly detect link faults and notify
OSPF so that it quickly responds to network topology changes. BFD support for OSPF
is disabled by default.
BFD and the BFD session parameters, as well as active or passive mode, can be configured at a global VRF level and at a neighbor or peer level.
Consider the following when configuring BFD for OSPF:
- OSPF initiates a BFD session when BFD is enabled at the OSPF global or interface level. Sessions are only useful when a neighbor state is 2-Way or more. Therefore, when a neighbor state transitions to 2-Way, OSPF initiates a BFD session. Similarly, when the neighbor state transitions to less than 2-Way, OSPF tears down the BFD session.
- OSPF registration with BFD is global across all VRFs.
- When OSPF receives notification from BFD of a state change to up, OSPF marks the interface level BFD state as up and stops the holdover timer, if it has been configured.
- When OSPF receives notification from BFD of a state change to admin down, OSPF marks the interface level BFD state as down.
- When OSPF receives notification from BFD of a state change to down, the OSPF neighbor transitions to a down state, forcing the necessary route calculation for the routes that are learned from the neighbor. If the holdover timer is configured, OSPF is not immediately notified about the down state and the holdover timer begins. If the configured holdover interval expires, OSPF is notified about the session failure and marks the interface level session as down, forcing the necessary route calculation for the routes that are learned from the neighbor.