HP A5830 series Configuration Manual page 154

Operation of BFD
Figure 41 BFD session establishment (on OSPF routers)
The process of BFD session establishment is as follows:
A protocol sends hello messages to discover neighbors and establish neighborships.
1.
After establishing neighborships, the protocol notifies BFD of the neighbor information, including
2.
destination and source addresses.
BFD uses the information to establish BFD sessions.
3.
Figure 42 BFD fault detection (on OSPF routers)
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Router A
Fault
BFD notifies the OSPF link failure
Backup link
The process of BFD fault detection is as follows:
BFD detects a link failure.
4.
BFD clears the neighbor session.
5.
BFD notifies the protocol of the failure.
6.
The protocol terminates the neighborship on the link.
7.
If a backup link is available, the protocol will use it to forward packets.
8.
No detection time resolution is defined in the BFD draft. Most devices supporting BFD provide detection
measured in milliseconds.
BFD detection methods
Single-hop detection—Detects the IP connectivity between two directly connected systems.
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Router B
BFD neighbors
OSPF neighbors