F3726, F3211, F3174, R5135, R3816-HP Firewalls and UTM Devices High Availability Configuration Guide-6PW100

240
from the peer within the negotiated BFD interval, BFD notifies a failure to the protocol, which takes
appropriate measures.
394BBFD session establishment
Figure 145 BFD session establishment (on OSPF routers)
As shown in 663HFigure 145, 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 146 BFD fault detection (on OSPF routers)
395BBFD 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.
5
OSPF neighbors
BFD neighbors
Router A
Router B
1
2
Fault
BFD notifies the OSPF link failure
33
4
Backup link