Re: exim, local resolver, host name lookups and IPv6
On Fri, 11 Apr 2008 18:09:27 +0200, "Bernhard R. Link"
<brlink@debian.org> wrote:
>* Marc Haber <mh+debian-devel@zugschlus.de> [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.
Another process on the local system might actually use IPv6 on the
local links, so I'd vouch for tweaking the system (or exim) to not
break if IPv6 is enabled but not fully connected.
>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'd call that a bug, since exim should have a "destination
unreachable" error upon trying to open the IPv6 connection in absence
of a IPv6 default route.
>> 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.
Yes, but why isn't exim satisfied with this being present for IPv4? If
it has a reason for wanting to do this for IPv6 as well, shouldn't we
make sure that the IPv6 lookups work locally as well as the IPv4
lookups do since we added 127.0.1.1 myhostname.localdomain myhostname
some years ago?
>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).
The only lookup that is still visible on the network (and only in some
cases that I haven't yet fully nailed down) is an AAAA lookup for the
local host name on exim startup.
Greetings
Marc
--
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Marc Haber | " Questions are the | Mailadresse im Header
Mannheim, Germany | Beginning of Wisdom " | http://www.zugschlus.de/
Nordisch by Nature | Lt. Worf, TNG "Rightful Heir" | Fon: *49 621 72739834
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