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Re: AAAA records to be added for root servers

2008-01-04 11:34:25


--On Monday, 31 December, 2007 10:05 -0800 Barbara Roseman
<barbara(_dot_)roseman(_at_)icann(_dot_)org> wrote:

apologies for cross-posting...

Which I have deleted on the grounds that most of  those lists
won't let me post anyway.  Feel free to forward if you think it
useful.

On 4 February 2008, IANA will add AAAA records for the IPv6
addresses of the four root servers whose operators have
requested it. A technical analysis of inserting IPv6 records
into the root has been done by a joint working group of
ICANN's Root Server System Advisory Committee and Security and
Stability Advisory Committee, a report of which can be found
at http://www.icann.org/committees/security/sac018.pdf.
Network operators should take whatever steps they feel
appropriate to prepare for the inclusion of AAAA records in
response to root queries.
...

While I _strongly_ favor this move, it is often, if not always,
useful to examine the applications that use the DNS as well as
effects on the DNS itself.  Because these changes to the root
are likely to facilitate the use of IPv6-native environments (as
distinguished of IPv6 systems in clearly IPv4 environments, as
the root servers have been to date), they may increase stresses
elsewhere.  Let me take email as an example of why this is
important.  Because there are no mail servers associated with
the root zone (there is not even a way to express a root-zone
email address), there should be no direct effect of these
changes.  But I think your announcement and comments should
anticipate possible indirect effects.

When an email address is specified, the domain is interpreted
for mail-routing purposes according to rules first laid out in
RFC 974, which has been updated in minor ways by RFC 1123 and
RFC 2821.  RFC 974 defined the MX RR.  The data associated with
the MX RR is simply a domain name, so MX records raise no issues
with IPv6.  However, there is also a rule that, if no MX records
are present at a particular node, the mail system looks for an A
RR at the same node and treats it as if its label appeared with
an MX preference of 0.  That default does not apply to AAAA
records, so it is necessary that operators understand that, if
mail systems are to be accessed using IPv6, they MUST have MX
records at the relevant nodes.  In addition, those MX records
should be configured with preferences appropriate to the
connectivity of the servers: expecting SMTP-senders to sort out
the relative appropriateness and priority from mixed IPv4 and
IPv6 addresses at the same preference level is, at best, likely
to be operationally unwise.

Again, there is no specific root server issue in any of this,
but it concerns me that none of the relevant committees or
studies appear to have considered the possible applications
implications of the change.

regards,
     john


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