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Configuring BFD
The term "interface" in this chapter refers to Layer 3 interfaces, including VLAN interfaces.
The following commands can be configured in Layer 2 aggregate interface view:
• bfd authentication-mode
• bfd detect-multiplier
• bfd min-receive-interval
• bfd min-transmit-interval
For more information about configuring BFD on Layer 2 aggregate interfaces, see Layer 2—LAN
Switching Configuration Guide.
Overview
Bidirectional forwarding detection (BFD) provides a general-purpose, standard, medium- and
protocol-independent fast failure detection mechanism. It can detect and monitor the connectivity of
links in IP to detect communication failures quickly so that measures can be taken to ensure service
continuity and enhance network availability.
BFD can uniformly and quickly detect the failures of the bidirectional forwarding paths between two
devices for upper-layer protocols such as routing protocols. The hello mechanism used by
upper-layer protocols needs seconds to detect a link failure, while BFD can provide detection
measured in milliseconds.
BFD can be used for single-hop and multihop detections.
• Single-hop detection—Detects the IP connectivity between two directly connected systems.
• Multihop detection—Detects any of the paths between two systems. These paths have
multiple hops, and might overlap.
BFD session establishment
Establishing a BFD session
BFD provides no neighbor discovery mechanism. Protocols that BFD services notify BFD of routers
to which it needs to establish sessions.
A BFD session is established as follows:
1. A protocol sends Hello messages to discover neighbors and establish neighborships.
2. After establishing a neighborship, the protocol notifies BFD of the neighbor information,
including destination and source addresses.
3. BFD uses the information to establish a BFD session.
Terminating a BFD session
When BFD detects a link failure:
1. BFD clears the neighbor session.
2. BFD notifies the protocol of the failure.
3. The protocol terminates the neighborship on the link.
4. If a backup link is available, the protocol will use it for communication.
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