Configuring bfd, Introduction to bfd, How bfd works – H3C Technologies H3C SR8800 User Manual
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Configuring BFD
NOTE:
The term
router in this document refers to both routers and Layer 3 switches.
Introduction to BFD
Routers must quickly detect communication failures so that measures can be taken in time to ensure
service continuity and enhance network availability.
The main 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 not all media types support hardware detection.
•
Hello mechanism—Routers can use the hello mechanism of a routing protocol to detect link failures.
The hello mechanism needs seconds to detect a link failure. On a high-speed interface, such as a
Gigabit interface, a failure that lasts for one second will cause a large quantity of data to be
dropped. The hello mechanism is unacceptable for delay-sensitive services such as voice service.
Moreover, this detection method largely relies on the routing protocol.
•
Other detection methods—Some protocols provide dedicated detection mechanisms, which
however, cannot be deployed for inter-system communications.
Bidirectional forwarding detection (BFD) provides a single mechanism to monitor links. With BFD, routers
can quickly detect communication failures and restore communications through backup paths.
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.