[Babel-users] Babel RTT settings for low and high latencies

[Marek Küthe]

Thank you for the explanations. I now clearly understand the options
better.

This is probably a slightly more stupid question, but I'm not very
familiar with metrics: A year ago you said [1] that bird had not yet
implemented "hysteresis on metrics" and therefore `rtt-min 1 rtt-max
1001 max-rtt-penalty 1000` could be unfavorable or problematic. Has bird
implemented this in the meantime? And what is the difference between
hysteresis and `rtt-decoy`?

[1] https://trubka.network.cz/pipermail/bird-users/2023-October/017216.html

On Wed, 17 Jul 2024 20:41:52 +0200
Juliusz Chroboczek <jch at irif.fr> wrote:

> > Thanks for the quick answers!
> > 
> > What should I set rtt-cost/max-rtt-penalty to?  
> 
> Max-rtt-penalty controls how much Babel will prefer routes with many links
> but low RTT to routes with few links but hight RTT.  The default is fairly
> conservative, meaning that RTT has only a very small influence on routing.
> You should set it to 96*n where n is the maximum number of extra links
> that you're willing to take in order to avoid one high-RTT link.
> 
> You should probably set it to 400 or so, and start tweaking from there.
> The value used by Nexedi (5000) looks quite extreme to me.
> 
> As to rtt-decay, the default value should be fine unless you have a mobile
> network.  Increase it in order to react faster to RTT variations, at the
> risk of route flaps every time the network has a hiccup.
> 
> -- Juliusz


-- 
Marek Küthe
m.k at mk16.de
er/ihm he/him
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