BFD - intervals and timers
When implementing Bidirectional Forwarding Detection (BFD) on a Cisco IOS device, there are several intervals and timers that must be configured. Specifically, we must configure:
interval- This specifies the rate in milliseconds at which BFD control packets will be sent to BFD peersmin_rx- This specifies the rate, in milliseconds, at which BFD control packets will be expected to be received from BFD peers.multiplier- This specifies the number of consecutive BFD control packets that must be missed from a peer before BFD declares that peer as unavailable.
Now these values are specified within the command like so:
bfd interval milliseconds min_rx milliseconds multiplier multiplier-value
However, according to the RFC definition of BFD, the actual intervals and values used between the BFD peers can vary somewhat. During negotiation, these may be modified. In addition, the RFC says that the actual interval and frequency at which control packets will be sent will change over time by up to 25% based on jitter values and on a level of randomness introduced to prevent self-synchronization.
For more details on BFD, take a look at:
- BFD echo mode and operation details
- BFD how an administrative change differs from a failure
- BFD one-arm echo
- BFD - slow-timers