HP VPN Firewall Appliances High Availability Configuration Guide

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How BFD works
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.
BFD session establishment
Figure 158 BFD session establishment (on OSPF routers)
As shown in Figure 158, 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 159 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.
5
OSPF neighbors
BFD neighbors
Router A
Router B
1
2
Fault
BFD notifies the OSPF link failure
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4
Backup link