Re: exim, local resolver, host name lookups and IPv6
* "Bernhard R. Link"
| 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 wonder if
http://patches.ubuntu.com/g/glibc/extracted/any/local-ipv6-lookup.diff
will help with that. It disables IPv6 lookups if the
af_hins->ai_family parameter in getaddrinfo is AF_UNSPEC and you don't
have an IPv6 address with scope > link (so if you don't have global or
site IPv6 addresses configured, you won't get IPv6 lookups from most
applications, while if you do, IPv6 works just fine.) The patch had
some unfortunate consequences when people used tunnels, see bug
441857. (Personally, I don't think supporting the use case of «I want
to use IPv6 to connect to localhost but I don't have any IPv6
addresses with scope:site or scope:global» is more interesting than
making IPv6 work for those who actually use it for talking to other
machines on the Internet and not bother those who doesn't use IPv6.)
The original reason for writing that patch is some cheap routers
(typically home DSL routers and the like) drop AAAA and A6 lookups on
the floor completely, leading to terrible DNS performance and leading
people to not loading the ipv6 module, something which is a bit of a
hack (and not very newbie friendly).
https://bugs.edge.launchpad.net/ubuntu/+source/netcfg/+bug/24828 has a
long discssion on some of the ramifications of blindly disabling
IPv6.
--
Tollef Fog Heen
UNIX is user friendly, it's just picky about who its friends are
Reply to: