HP 6125G HP 6125G & 6125G/XG Blade Switches High Availability Configur - Page 182

Configuring BFD, BFD overview, How BFD works, Operation of BFD

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Configuring BFD The term router in the BFD feature refers to both routers and Layer 3 switches. BFD overview Devices must quickly detect communication failures so that measures can be taken promptly 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-Devices can use the hello mechanism of a routing protocol to detect link failures, which has a failure detection rate in seconds. 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. However, they cannot be deployed for inter-system communications. Bidirectional forwarding detection (BFD) provides a single mechanism to monitor links. With BFD, devices 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. 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 45 BFD session establishment (on OSPF routers) 175

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175
Configuring BFD
The term
router
in the BFD feature refers to both routers and Layer 3 switches.
BFD overview
Devices must quickly detect communication failures so that measures can be taken promptly 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
—Devices can use the hello mechanism of a routing protocol to detect link failures,
which has a failure detection rate in seconds. 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. However,
they cannot be deployed for inter-system communications.
Bidirectional forwarding detection (BFD) provides a single mechanism to monitor links. With BFD,
devices 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.
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 45
BFD session establishment (on OSPF routers)