From: Alexander Bluhm <bluhm@openbsd.org>
Subject: Re: ipv4 icmp_reflect() source address selection optimisation
To: David Gwynne <david@gwynne.id.au>
Cc: tech@openbsd.org
Date: Fri, 9 Aug 2024 11:15:34 +0200

On Fri, Aug 09, 2024 at 10:40:11AM +1000, David Gwynne wrote:
> tl;dr: i believe this change would let us simplify pf_route (the
> loopback ip handling specifically), so it's worth it.

In contrast I have worked on all the corner cases in 15 years to
make it work.  Maybe not the best solution, but it works.  I fear
that at our customers somethig will break if we change behavior
just because we think it looks better.

In this particular case I think using the first addreess as source
address is wrong.  IPv4 source address selection should be done
with a route lookup.  Basically what in_pcbselsrc() does.  And using
the route interface address seems reasonable to me.

bluhm