H3C Technologies H3C S7500E Series Switches - Manual (Page 174)

11-2
How BFD Works
BFD provides a general-purpose, standard, medium- and protocol-independent fast failure
detection mechanism. It can uniformly and quickly detect the failures of the bidirectional
forwarding paths between two routers for protocols, such as routing protocols and Multiprotocol
Label Switching (MPLS).
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.
Operation of BFD
Figure 11-1 BFD session establishment (on OSPF routers)
BFD session establishment (as shown in the above figure):
z A protocol sends Hello messages to discover neighbors and establish neighborships.
z After establishing neighborships, the protocol notifies BFD of the neighbor information,
including destination and source addresses.
z BFD uses the information to establish BFD sessions.
Figure 11-2 BFD fault detection (on OSPF routers)
BFD fault detection (as shown in the above figure):
1) BFD detects a link failure.
2) BFD clears the neighbor session.