H3C Technologies H3C MSR 50 - Manual (Page 13)

5
BFD session establishment
Figure 1 BFD session establishment (on OSPF routers)
As shown in Figure 1 , BFD sessions are established as follows:
1. A protocol sends Hello messages to discover neighbors and establish neighborships.
2. After establishing neighborships, the protocol notifies BFD of the neighbor information, including
destination and source addresses.
3. BFD uses the information to establish BFD sessions.
Figure 2 BFD fault detection (on OSPF routers)
BFD fault detection
The BFD fault detection process is as follows:
1. BFD detects a link failure.
2. BFD clears the neighbor session.
3. BFD notifies the protocol of the failure.
4. The protocol terminates the neighborship on the link.
5. If a backup link is available, the protocol will use it to forward packets.
No detection time resolution is defined in the BFD draft. Most devices supporting BFD provide detection
measured in milliseconds.
BFD detection methods
BFD detection methods include the following:
5
OSPF neighbors
BFD neighbors
Router A Router B
1
2
Fault
BFD notifies the OSPF link failure
3 3
4
Backup link