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BFD (Bidirectional Forwarding Detection)

BFD is a network protocol designed to provide rapid detection of failures in the forwarding path between two devices. It operates independently of the underlying transport protocol and provides low-latency failure detection. It is lightweight and allows the network to react quickly to failures, improving convergence times for protocols like BGP and others.

BFD establishes a session between two devices, monitoring the liveness of a specific path. Each device exchanges BFD control packets at defined intervals (transmit and receive intervals). If a failure is detected, BFD immediately notifies higher-layer protocols (like BGP), which can quickly reroute traffic.

Key Configuration Parameters

  • Minimum TX Interval: the minimum interval in milliseconds between BFD control packets sent by a device. This defines how frequently packets are transmitted.
  • Minimum RX Interval: the minimum interval in milliseconds that a device expects to receive BFD control packets from its peer.
  • Detection Multiplier: the number of consecutive missed BFD control packets required to declare the session down.
  • Hold time: the time to wait before declaring a session down if the detection multiplier threshold has been reached.

Like multi-hop BGP, BFD can also operates in a multi-hop mode when the peer is multiple hops away.

Typical BFD Values:

  • Minimum TX Interval: 300ms
  • Minimum RX Interval: 300ms
  • Detection Multiplier: 3 (meaning the session is considered down after 3 missed packets)

Usage

Create a BFD configuration object with wanted values. Set the BFD configuration to use when creating or editing a BGP session (IXP or direct).