Configuring Bfd; Introduction To Bfd; How Bfd Works - HPE FlexNetwork HSR6800 series Configuration Manual

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.
BFD session establishment
Figure 52 BFD session establishment (on OSPF routers)
As shown in
1. A protocol sends Hello messages to discover neighbors and establish neighborships.
Figure 52, BFD sessions are established as follows:
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