Subject: Re: [dnsop] Questions about IPv4 or IPv6 DNS server

From: Pekka Savola <[email-masked]>
Date: Wed, 1 Nov 2006 09:52:52 +0200 (EET)

On Tue, 31 Oct 2006, Edward Lewis wrote:
> At 16:34 +0000 10/31/06, Jeroen Massar wrote:
> 
> >Like any IPv4 -> IPv6 transition mechanism: first try IPv6, then try IPv4.
> 
> There is the option to try both simultaneously.  A query for the A RR can be
> sent in parallel to the AAAA RR.  This is better from the point of view of the
> application user, there isn't a need to wait for a time out.  On the other
> hand, this makes the application developer's job harder - having to juggle two
> potential answers and connections starting up (assuming TCP).

Note that the original question was about which DNS _server_ to query 
first, not which RR type to query first.

I believe most implementations send the queries in the order the 
servers have been listed in /etc/resolv.conf or equivalent, and this 
decision algorithm doesn't care whether the address is v4 or v6.

As for the latter issue, RFC 4472 section 5.1 discusses this a bit.

-- 
Pekka Savola                 "You each name yourselves king, yet the
Netcore Oy                    kingdom bleeds."
Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings
.
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---

From: Edward Lewis <[email-masked]>
Date: Wed, 1 Nov 2006 08:55:00 -0500

At 4:58 PM +0800 11/1/06, Blue wrote:
>Hi,
>
>For statically and manually configured DNS server list, the resolver won't
>have problems in choosing IPv4/IPv6 servers. Like you've said, the sequence
>is supposed to be based on the configuration file. However, when we have
>dynamic DNS v4/v6 server list from DHCPv4/DHCPv6, the resolver needs to
>decide which server to request first.
>
>BR,
>
>Yi-Wen

In this case, my answer would be a bit different from what I wrote 
earlier.  If it is a matter of which transport is used for a stub 
resolver (something that reads a static list) to reach a local name 
server, then the administrator should configure using the more stable 
transport first.  An administrator can judge that as usually you are 
only traversing one network from stub to local name server.  If the 
administrator wants to shift traffic to IPv6, then that is configured 
first.

To clarify my previous messages - the reason I talk about retrieving 
address records is that before you can reach a server you have to 
have the address records.  When an NS record is read and you get the 
domain name, you have the choice to ask for one or the other, or both 
address types.  From that you open transport points (ports in UDP). 
If you only get the AAAA record, you can't try the IPv4 transport.

I am not trying to discourage the use of IPv6 through my disagreement 
with trying "IPv6 first, IPv4 second."  In my experience with the 
state of IPv6 routing across a wide area, the IPv6 backbone (such as 
it is) is still in being formed.  And until there is an authoritative 
AAAA in the root-servers.net zone for any of the root servers the DNS 
(system) is still "fractured" in IPv6 space.  (As in, you have to go 
through IPv4 to get anywhere.)
-- 
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Edward Lewis                                                +1-571-434-5468
NeuStar

Secrets of Success #107: Why arrive at 7am for the good parking space?
Come in at 11am while the early birds drive out to lunch.
.
dnsop resources:_____________________________________________________
web user interface: http://darkwing.uoregon.edu/~llynch/dnsop.html
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