babel rtt in bird: How to set the RTT equal to the latency?

[Juliusz Chroboczek]

> 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