bird-1.6.8: Withdrawals during an enhanced route-refresh process

[Garri Djavadyan]

On Fri, 2022-10-14 at 16:10 +0200, Ondrej Zajicek wrote:
> On Fri, Oct 14, 2022 at 01:28:27AM +0200, Garri Djavadyan via Bird-
> users wrote:
> > Hello everyone,
> > 
> > I noticed that the legacy Bird version behaves strangely while it
> > is in
> > an enhanced route-refreshing process, but I am not sure whether it
> > is a
> > known/expected behaviour for version 1.6.8. Namely, right after a
> > 1.6.8
> > peers sends a BoRR message, it also sends withdrawals for the
> > prefixes
> > it received from that same peer. For example, below is the output
> > from
> > two Bird peers (1.6.8 and 2.0.10):
> > 
> > So, I am just curious if it is a bug or some architectural
> > limitation
> > of Bird-1.6. If I understand correctly, there are two problems
> > here:
> 
> Hello
> 
> Yes, it is expected, although unnecessary. The route feeding code
> just
> send updates or withdraws and does not consider whether it is initial
> feed, regular route refresh, or enhanced route-refresh.
> 
> In BIRD 2.0.10, we keep a bitmap of routes that were announced, so we
> do
> not send withdraws for ones that were not announced before, but we
> would
> AFAIK send unnecessary withdraws during enhanced route-refresh (for
> routes
> that were announced before).
> 

Indeed, BIRD 2.0.10 also sends redundant/explicit withdrawals for
previously announced prefixes during ERR.

Thank you for the details, Ondrej.


Garri