H3C LS-3100-52P-OVS-H3 Operation Manual - page 822
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BFD provides no neighbor discovery mechanism. Protocols that BFD services notify BFD of routers to
which it needs to establish sessions. After a session is established, if no BFD control packet is received
from the peer within the negotiated BFD interval, BFD notifies a failure to the protocol, which takes
appropriate measures.
Operation of BFD
Figure 1-1 BFD session establishment
OSPF neighbors
BFD neighbors
Router A
Router B
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2
3
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OSPF advertises the BFD neighbor relationship
BFD session establishment (as shown in the above figure):
z
A protocol sends Hello messages to discover neighbors and establish neighborships.
z
After establishing neighborships, the protocol notifies BFD of the neighbor information, including
destination and source addresses.
z
BFD uses the information to establish BFD sessions.
Figure 1-2 BFD fault detection
BFD fault detection (as shown in the above figure):
z
Upon detection of a link failure, BFD clears the session and notifies the protocol of the failure.
z
The protocol terminates the neighborship on the link.
z
If a backup link is available, the protocol will use it to forward packets.