H3C Technologies H3C MSR 50 - Manual (Page 12)

4
Configuring BFD
Introduction to BFD
Devices must detect communication failures quickly so that measures can be taken in time to ensure
service continuity and enhance network availability.
Fault detection methods include the following:
• Hardware detection—Detects link failures by sending hardware detection signals, such as
synchronous digital hierarchy (SDH) alarms. Hardware detection can quickly detect link failures,
but is not supported by all media types.
• Hello mechanism—Devices can use the hello mechanism of a routing protocol to detect link failures.
The hello mechanism takes seconds to detect a link failure. However, that detection rate is too slow
for voice services and other delay-sensitive services. It is also too slow for high-speed data
transmission, such as Gigabit data transmission, where a detection rate slower than one second will
cause a large quantity of data to be dropped. This detection method is dependent on the routing
protocol.
• Other detection methods—Some protocols provide dedicated detection mechanisms. However,
these are difficult to deploy for inter-system communications.
Bidirectional forwarding detection (BFD) provides a single mechanism to quickly detect and monitor the
connectivity of links or IP forwarding in networks. To improve network performance, devices must quickly
detect communication failures and restore communication through backup paths as soon as possible.
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.