RFT: Babel RTT extension in Bird

[Stefan Haller]

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.

> 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.

Best regards,
Stefan Haller