RFT: Babel RTT extension in Bird

[Toke Høiland-Jørgensen]

Stefan Haller <stefan.haller at stha.de> writes:

> On Sat, Apr 23, 2022 at 11:20:57PM +0200, Toke Høiland-Jørgensen wrote:
>> > (3) Due to route flapping I tried to increase "metric decay" to 60s.
>> > After running "birdc configure" the values became very large for one
>> > link (on one side only).
>> 
>> Which values become very large? And is this persistent? What kind of
>> route flapping were you seeing?
>
> The routes were "flapping" simply because the RTT were very similar and
> sometimes one next hop wins, sometimes the other. I don't think this is
> a problem, but expected behaviour. I was just trying out the "metric
> decay" setting to check if routing tables do change less often. Seems to
> work.

Ah, right. When you said 'flapping' I took that to mean 'at very short
timescales', but if the damping is working that's great!

>> Hmm, so that initial value is '-973' as a 32-bit unsigned int. So looks
>> like there's an overflow in the RTT calculation. I'll add some sanity
>> checks to make sure this doesn't happen (as indeed babeld has as well).
>
> I did not observe this problem with the new version anymore.
>
>> I force-pushed an updated version to the same branch which fixes the
>> issues you noted above apart from the route flap one. Inspired by the
>> first issue noted above, I also added a separate config parameter to
>> control the *sending* of timestamps, which defaults to on.
>
> I am running the new version since Tuesday and everything looks good
> so far.

Excellent! Thanks again for testing - let me know if you run into any
other issues :)

-Toke