DNS Behaviour - Dual Stack Clients

Paul Stewart paul at paulstewart.org
Fri Mar 19 03:40:39 CET 2010

Excellent - I appreciate this information.  ;)  This is very helpful to figure out what needs to be done first in our IPv6 conversions.  Servers were last on the list and network was first... and we're migrating from Cisco over to Juniper on most fronts so this was a great time to start working on all aspects of our network.  Since we require every aspect of our network to have a hostname forward and reverse we thought this a great time to update things with IPv6 in mind...

Take care,


-----Original Message-----
From: Brian E Carpenter [mailto:brian.e.carpenter at gmail.com] 
Sent: March-18-10 9:24 PM
To: Paul Stewart
Cc: ipv6-ops at lists.cluenet.de
Subject: Re: DNS Behaviour - Dual Stack Clients


On 2010-03-19 12:02, Doug Barton wrote:
> On 03/18/10 15:55, Paul Stewart wrote:
>> Thank you for the reply... so just to clarify further...
>> A remote client or name server queries our nameserver (which is only reachable via IPv4).  Our name server replies with A and AAAA records in the lookup.  If the remote client is IPv6 capable will it ignore the AAAA information because it was only able to get the query answered via IPv4?  I believe this is what you're saying - again, just looking to clarify ;)
> Um, no, what I'm saying is actually the opposite. How the client
> receives the address records has nothing to do with what it does with
> them. If the client is IPv6-capable, and receives AAAAs, it will use
> them. The client does not even know how the resolving nameserver
> retrieved the records, nor could it find out.

To be even more explicit, clients that can only resolve FQDNs by
DNS-over-IPv4, but that speak IPv6 and make use of AAAA records,
are common; I'm using one right now (XP, to give it a name).
My home ISP only provides DNS-over-IPv4 but happily serves up
AAAA records:

Default Server:  dns1.orcon.net.nz
> set type=AAAA
> www.ietf.org
Server:  dns1.orcon.net.nz

Non-authoritative answer:
www.ietf.org    AAAA IPv6 address = 2001:1890:1112:1::20

(I get my home v6 connectivity by a tunnel, but exactly the
same thing happens on an XP client with native v6.)


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