Strange IPv6 DNS lookups

[Reber, Simon]

Kenneth,

Just one question about this problem:
	Do you report any performance problems or latency on your system
because of this issue?

The reason why I am asking is that I hardly remember seeing that before.
But I haven't noticed any problem. I've just realized that the lookup
covers both IPv6 and IPv4.

An other question would be which version of RedHat you are running on?

Cheers,
Si

>-----Original Message-----
>From: redhat-list-bounces at redhat.com 
>[mailto:redhat-list-bounces at redhat.com] On Behalf Of Kenneth Holter
>Sent: Friday, March 20, 2009 8:18 AM
>To: General Red Hat Linux discussion list
>Subject: Re: Strange IPv6 DNS lookups
>
>Thanks for the advice.
>
>I've followed the steps you outlined below, but the problem 
>unfortunately
>persists. I've learned that most packages on the system are 
>compiled with
>IPv6 support, so from what I can tell this is what is usually 
>happening:
>
>   1. The client process (can be more or less whatever process 
>running on
>   the linux box) issues a AAAA DNS query for the FQDN *
>   server1.example-prod.com*
>   2. The DNS server drops the package, so the linux box 
>iterates through
>   the "search" entries in /etc/resolv.conf, adding the 
>entries found here to
>   the FQDN. This results in the bizarre queries mentioned in 
>my first post.
>   3. When AAAA record queries does not return a valid answer, 
>a normal A
>   query is made. This query returns the corret result.
>
>Say I have two entries in the "search" section of 
>/etc/resolv.conf, I will
>end up with the linux box issuing 3 unsuccessful AAAA queries for every
>successful A query. This causes a great amount of overhead on 
>the DNS server
>(or the linux box if caching is used).
>
>I'm sure we're not the only ones having to deal with this issue, so any
>advice on how to proceed will be greatly appreciated.
>
>Regards,
>Kenneth
>
>
>
>On 3/11/09, Reber, Simon <simon.reber at roche.com> wrote:
>
>> Hey Kenneth,
>>
>> Try to fully disable IPv6 while adding:
>>
>>        alias net-pf-10 off
>>        alias ipv6 off
>>
>> to /etc/modprobe.conf and to /etc/sysconfig/network
>>
>>        NETWORKING_IPV6=no
>>
>> This should probably solve the problem (at least IPv6 is turned off)
>>
>> Cheers,
>> Si
>>
>> >-----Original Message-----
>> >From: redhat-list-bounces at redhat.com
>> >[mailto:redhat-list-bounces at redhat.com] On Behalf Of Kenneth Holter
>> >Sent: Monday, March 09, 2009 4:17 PM
>> >To: redhat-list at redhat.com
>> >Subject: Strange IPv6 DNS lookups
>> >
>> >Hello all.
>> >
>> >
>> >Several of our RHEL-servers are issuing strange DNS lookups.
>> >Consider this
>> >example:
>> >
>> >
>> >*  1   0.000000   1.2.3.4 -> 5.6.7.8   DNS Standard query AAAA **
>> >server1.example-prod.com* <http://server1.example-prod.com/>*
>> >  9   0.007891   1.2.3.4 -> 5.6.7.8   DNS Standard query AAAA
>> >server1.example-prod.com.example-test.local
>> > 11   0.092904   1.2.3.4 -> 5.6.7.82   DNS Standard query A
>> >server1.example-prod.com
>> > 12   0.093356   5.6.7.8 -> 1.2.3.4   DNS Standard query
>> >response A 1.2.3.4
>> >*
>> >
>> >>From what I can tell, the client first issues two IPv6 DNS
>> >lookups, before
>> >falling back to IPv4 lookup. We're not running IPv6 (and our
>> >DNS servers do
>> >not support IPv6 lookups), so the client is not getting and
>> >answer before
>> >issuing the IPv4 lookup.
>> >
>> >I've very puzzled by the second query, in which the FQDN of
>> >the lookup query
>> >is appended another domain. I've noticed that the appended
>> >domain may be
>> >both the same domain name (i.e.
>> >server1.example-prod-com.example-prod.com)
>> >or another domain as in the example above.
>> >Does anyone have a clue as to why such bizarre queries are
>> >performed by the
>> >client?
>> >
>> >Since we're not running IPv6, I have simply disabled it for 
>this server
>> >(grepping "lsmod" does not return any "ipv6" results). Yet 
>the problem
>> >remains. Does the DNS lookup library automatically issue IPv6
>> >queries before
>> >issuing IPv4 queries? Is there a way to disable IPv6 lookups?
>> >
>> >
>> >Regards,
>> >Kenneth Holter
>> >--
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