Bidirectional Forwarding Detection

General information on “Bidirectional Forwarding Detection”:

• Protocol-independent mechanism to massively speed up convergence
• Uses udp/3784 (dest. port) and udp/49152-65535 (src. port)
• Failure detection time can be as low as 150 seconds
• Works by exchanging HELLO packets on the specific link where the routing protocol runs
• Multiple protocols can register to the same single BFD process
• Example: BFD is activated between two routers running EIGRP…
  • Without BFD: The holdtimer needs to expire before EIGRP notices that the neighbor is down.
  • With BFD: The EIGRP process will get immediately notified that the neighbor is not reachable anymore.

“Bidirectional Forwarding Detection” CLI configuration commands:

## Enabling BFD on an interface
Router(config)# interface <if>
Router(config-if)# bfd interval <milliseconds> min_rx <milliseconds> multiplier <value>

## Enabling BFD for EIGRP (classic mode)
Router(config-router)# bfd all-interfaces

## Enabling BFD for EIGRP (named mode)
Router(config-router-af)# af-interface <if>
Router(config-router-af-interface)# bfd

## Enabling BFD for OSPFv2
Router(config-router)# bfd all-interfaces

## Enabling BFD for OSPFv3 (configured per AF)
Router(config-router-af)# bfd all-interfaces

## Enabling BFD for BGP
Router(config-router)# neighbor <ip> fall-over bfd

“Bidirectional Forwarding Detection” CLI show commands:

## Showing BFD neighbors and stats
Router# show bfd neighbors