How are you configuring BFD timers?

Wed Mar 21 20:38:23 UTC 2018

:: For those running BFD on your land-based point-to-point links, 
:: I’m interested in hearing about what factors you consider when 
:: deciding how to configure your timers and multiplier.

It has been a while since I used BFD, but I remember trying to get 
it as close to what I wanted and then fine tuning it over time.
For example, sometimes it would take down the session when I didn't 
want it to and I had to turn the knobs a bit.  So another thing to
consider is your initial design choice is likely to change over
time.

scott

--- jason+nanog at lixfeld.ca wrote:
From: Jason Lixfeld <jason+nanog at lixfeld.ca>

For those running BFD on your land-based point-to-point links, I’m interested in hearing about what factors you consider when deciding how to configure your timers and multiplier.

On paper, BFD between two devices over a local or metro dark fibre or wave seems pretty trivial:  Assuming your gear can a) support echo mode b) hardware offloads echo processing c) automatically treats echos as vital and puts them into the appropriate high priority queue, then setting the timers down to their lowest possible values (3ms on some of the gear that I’ve seen) and some low multiplier seems more than reasonable.  But?

From another angle, your link isn’t dark fibre or a wave but, for example, ethernet over some sort of IP based L2 Transport, and is still a low (sub 1ms) one-way latency local or metro link.  How do you set your timers, and what do you base that on?

From yet another angle, what if your link is a long-haul wave, or for that matter a wave of any distance that imposes a one-way latency that is higher than the minimum tx and rx timers that are supported by your gear?  We’ll assume an unprotected wave, because I’m sure if it’s protected, you have no choice but to consider the one-way latency of the longest of the two segments.

I made some assumptions above about support for echo mode and hardware offload, but what if (some of) your gear doesn’t support some or all of that stuff?  How do you factor your configuration decisions?

Thanks!