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BFD – Bi-Directional Forwarding Detection

  • BFD is for faster detection of failures.
  • It is independent of routing protocols, so it can be used with any protocol (known as client protocol).
  • BFD makes session based on request of the Client Protocol.
  • It is always Unicast and point to point in nature.
  • It has UDP port no 3784.
  • There are two modes in BFD :-
    • Asynchronous – Control packets on fixed interval and down if misses.
    • Demand – Never ever used.

It has a special feature known as ECHO MODE (on UDP port 3784) where device will return the ECHO packets without processing them. So in short we can say BFD ECHO mode travels only in data plane, which enables the Fast detection possible without any extra overhead on CPU/Control Plane.

  • BFD has timers as below :-
    • BFD Multiplier – It is same as Dead interval.
    • Min Rx – rate at which BFD will expect the packets
    • Interval – rate at which BFD will send the packets

BFD will negotiate the HIGHER timer if the timers mismatch on peer NEs.

BFD States :-

  1. DOWN ———-> INIT ————> UP

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