Re: exim, local resolver, host name lookups and IPv6
* Marc Haber <firstname.lastname@example.org> [080411 16:41]:
> To avoid the extra DNS lookups, the Exim packages have a Debconf
> option to configure exim for "minimal DNS usage", which hardcodes the
> hostname into Exim's configuration at package configuration time. This
> was necessary since - without this option - exim looks up its own host
> name in the DNS even when a completely local operation is invoked.
I think the main problem is that Debian is by default setting up those
ipv6 stuff into the interface even when you are in an pure ipv4
environment. That way exim4 cannot do anything to avoid ipv6 stuff
and evil things like this can happen.
I don't think that is only limited to additional lookups. I think I've
also seen a message not being sent on etch, because the target host
also had a AAAA record. (At least I think that is the reason, after
disabling ipv6 in exim4.conf it was sent).
> I feel that the IPv6 issue is the same that led us to invoke the
> 127.0.1.1 hack for IPv4, and if the answer to the IPv6 issue is "fix
> exim", then _how_ should exim be fixed, and why wasn't the answer to
> the IPv4 version of the issue "fix exim"?
I think it is not an issue of only exim. Many services want to have a
name and prefer some canonical or fully qualified hostname.
Which useally means something like a gethostbyname or doing a resolv
forward and backward manually.
So I fear the solution might not easily be reachable globally. If exim
can be fixed here depends on why it does does lookups. (As far as I
remember it does not only lookup the hostname, but also things like
"localhost", dunno whether this is caused by the term showing up in
some configuration file or if it is something hardcoded).
Bernhard R. Link