F3726, F3211, F3174, R5135, R3816-HP Firewalls and UTM Devices High Availability Configuration Guide-6PW100

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11BConfiguring BFD
The term "router" in this document refers to both routers and routing-capable firewalls and UTM devices.
BFD can be configured only at the CLI.
65B
Feature and hardware compatibility
Hardware BFD com
p
atible
F1000-A-EI/F1000-S-EI No
F1000-E No
F5000 Yes
Firewall module No
U200-A No
U200-S No
Bidirectional forwarding detection (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.
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Overview
Devices must detect communication failures quickly so that measures can be taken in time to ensure
service continuity and enhance network availability.
The following lists some common fault detection methods:
• 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.
• BFD—provides a single mechanism to quickly detect faults on links between devices.
215BHow 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