BFD session establishment and termination
BFD does not provide any neighbor discovery mechanisms. The upper protocol notifies BFD of the routers to which it needs to establish sessions. After establishing a neighborship, the upper protocol notifies BFD of the neighbor information, including destination and source addresses. BFD uses the information to establish a BFD session.
When BFD detects a link failure, it performs the following tasks:
BFD clears the neighbor session and notifies the protocol of the failure.
The protocol terminates the neighborship on the link.
If a backup link is available, the protocol will use it for communication.