babel rtt in bird: How to set the RTT equal to the latency?
Hello, I have seen that in bird 2.14 the babel rtt extension has been implemented. I was very happy about that! Currently I use the following setting of babeld for rtt: ``` default type tunnel rtt-min 1 rtt-max 1001 max-rtt-penalty 1000 enable-timestamps true ``` It causes the RTT to be equal to the latency to the other node. I have seen that there is both rtt-min and rtt-max setting in bird, but no max-rtt-penalty. So my question is how would I represent the above expression in bird? I would be very happy to get an answer! Greetings Marek Küthe -- Marek Küthe m.k@mk16.de er/ihm he/him
Hi Marek, On Wed, Oct 18, 2023 at 10:49:34PM +0200, Marek Küthe wrote:
I have seen that there is both rtt-min and rtt-max setting in bird, but no max-rtt-penalty. So my question is how would I represent the above expression in bird?
The `rtt cost` option is the equivalent in bird. --Daniel
default type tunnel rtt-min 1 rtt-max 1001 max-rtt-penalty 1000 enable-timestamps true ``` It causes the RTT to be equal to the latency to the other node.
More precisely, it causes the cost to be equal to the RTT. The recommended default values are much more conservative: rtt-min 10 rtt-max 120 This causes RTTs below 10ms to be considered as all equally good, and links above 120ms to all be considered as equally bad. The result is that minor oscillations of the metrics of high-rtt links do not cause cost fluctuations, which avoids oscillations. It is of course possible that these values are not appropriate in your network; however, I fear that the extremely aggressive values that you describe above may cause unnecessary oscillations, especially since BIRD does not yet implement hysteresis on metrics. -- Juliusz
On Fri, 27 Oct 2023 17:35:24 +0200 Juliusz Chroboczek <jch@irif.fr> wrote:
The recommended default values are much more conservative:
rtt-min 10 rtt-max 120
This causes RTTs below 10ms to be considered as all equally good, and links above 120ms to all be considered as equally bad. The result is that minor oscillations of the metrics of high-rtt links do not cause cost fluctuations, which avoids oscillations.
Thanks for the explanation! I have to admit that I didn't quite know what the default values did before.
It is of course possible that these values are not appropriate in your network; however, I fear that the extremely aggressive values that you describe above may cause unnecessary oscillations, especially since BIRD does not yet implement hysteresis on metrics.
I hope it's okay if I ask something about such an old e-mail. I have a network where sometimes it comes to an RTT of 1ms (when nodes are next to each other) and sometimes it comes to 300ms (Europe <-> Hong Kong). In this case I would use something like `rtt-max 300`. Which rtt-cost would you recommend?
-- Juliusz
-- Marek Küthe m.k@mk16.de er/ihm he/him
participants (3)
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Daniel Gröber -
Juliusz Chroboczek -
Marek Küthe