HP 4800G Series Configuration Manual page 1587

Operation of BFD
Figure 1-1 BFD session establishment
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Router A
BFD neighbors
OSPF advertises the BFD neighbor relationship
BFD session establishment (as shown in the above figure):
A protocol sends Hello messages to discover neighbors and establish neighborships.
After establishing neighborships, the protocol notifies BFD of the neighbor information, including
destination and source addresses.
BFD uses the information to establish BFD sessions.
Figure 1-2 BFD fault detection
BFD fault detection (as shown in the above figure):
Upon detection of a link failure, BFD clears the 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 to forward packets.
No detection time resolution is defined in the BFD draft. At present, most devices supporting BFD
provide detection measured in milliseconds.
BFD session modes
Control packet mode: Both ends of the link exchange BFD control packets to monitor link status.
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2
1
Router B
OSPF neighbors
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