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

[Ondrej Zajicek]

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).

-- 
Elen sila lumenn' omentielvo

Ondrej 'Santiago' Zajicek (email: santiago at crfreenet.org)
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"To err is human -- to blame it on a computer is even more so."