Bug#608061: libc6: dns-lookup unusable in mixed ipv4/ipv6-networks

[Felix Schueller <felix@fschueller.eu>]

Hello,

thanks for your quick reply.

>Your trace proves nothing, this is a tcpdump with no data inside, you
>give actually no way to reproduce the problem.

Sorry for that, it took me to long find at least an idea whats wrong,
so i forgot to use a better dump (strace didn't show something
interesting for me)

After submitting this bug i disscussed it once again with a friend, and
i found one reason for this problem. As i said, i've installed squeeze
two times, on different machines in different networks. Both in mixed
ipv4/ipv6 networks, working normaly with lenny, but (as i know now) in
both networks the (recursive) dns-server is an rather old version of
maradns as (1.2X) witch answers to AAAA lookups normaly if they exists,
but answers strange if no AAAA exists. (the full tcpdump looks, as if
maradns puts parts of the SOA-info in this answer)

libc6 in lenny seams to ignore this, but the libc6 in squeeze reads this
as "not found".

So im not longer shure weather this is a bug, or just something to be
dokumented. (i searched a lot, and found not much about problem like
this, apart from an old bug (#541167 from 2009) against this pakage)

But if you need any further informations, the dns here is
now a newer version of maradns and the Problem is gone, but the other
machine is still behind the older version, and i can give you some
better details (in two weeks) bevor upgrading this server.

>> When looking up an ip-address on an ipv6-enabled system, libc tries to
>> find an A and an AAAA-record. But, if some machine has only an A but
>> no AAAA record it returns host-not-found (see tcpdump below)

>> So one can only connect (with e.g. iceweasel, w3m, telnet) to hosts
>> with both A and AAAA records (or server with cname-records)

>> On an ipv4-only machine this can be "solved" by disabling ipv6
>> completly, but on a dualstack-machine, i found no way to fix this.

>> I found this on bug on two ways, an installing squeeze via d-i (the
>> ipv4 only machine) and via upgrading from lenny to squeeze

[...]

>Have you modified your /etc/gai.conf, are you using nscd with hosts
>caching ?

No to both.

By
  Felix