From: Amos Jeffries <squid3@treenet.co.nz>
To: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>
Cc: Ed W <lists@wildgooses.com>, netfilter <netfilter@vger.kernel.org>
Subject: Re: ipset causes reverse dns lookups?
Date: Tue, 17 Apr 2012 01:08:59 +1200 [thread overview]
Message-ID: <4F8C19EB.4070803@treenet.co.nz> (raw)
In-Reply-To: <alpine.DEB.2.00.1204161126050.20321@blackhole.kfki.hu>
On 16/04/2012 9:55 p.m., Jozsef Kadlecsik wrote:
> On Mon, 16 Apr 2012, Ed W wrote:
>
>> On 16/04/2012 09:08, Jozsef Kadlecsik wrote:
>>> Hostname and IP address are both supported as input and resolved
>>> internally by getaddrinfo. That can generate DNS lookups, depeding on the
>>> resolver library. What kind of system do you use, with which
>>> resolver/libc version?
>> Thanks so much for replying!
>>
>> This is a uclibc 0.9.33.1 system, x86. Resolver chain is /etc/hosts, then dns.
>> Local dnsmasq is installed.
>>
>> I can very clearly observe that on something like "ipset add", if I add
>> something that isn't quite an IP address then it generates a name lookup. What
>> I'm confused by is why the reverse ip lookup for the ip address? I have
>> traced it back I think to the parser.c code, but I concede I'm stuck
>> understanding even what is generating the lookup? You mention resolver, so
>> presumably it's a side effect of some other call, but could you spare a minute
>> to explain the trigger please? (just interested in the background in case it
>> occurs elsewhere?)
> That comes from the implementation of "getaddrinfo" in uclibc then. ipset
> itself does not force reverse DNS lookups.
FWIW, I have recently been dealing with user complains with other
software when built with uclibc. The uclibc implementation has been
caught ignoring AI_NUMERICHOST and performing full remote resolution
when passed numeric IPs for conversion.
AYJ
next prev parent reply other threads:[~2012-04-16 13:08 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-04-15 23:26 ipset causes reverse dns lookups? Ed W
2012-04-16 1:15 ` Ed W
2012-04-16 3:23 ` Ed W
2012-04-16 8:08 ` Jozsef Kadlecsik
2012-04-16 8:37 ` Ed W
2012-04-16 9:55 ` Jozsef Kadlecsik
2012-04-16 13:08 ` Amos Jeffries [this message]
2012-04-16 13:21 ` Jozsef Kadlecsik
2012-04-16 13:14 ` Ed W
2012-04-16 13:20 ` Jozsef Kadlecsik
[not found] ` <4F8C1E78.6030202@wildgooses.com>
[not found] ` <alpine.DEB.2.00.1204161548170.20321@blackhole.kfki.hu>
2012-04-16 22:05 ` Ed W
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