[dns-wg] AAAA lookup misbehaviour

At the last RIPE meeting I was given an action item:

	Write up a draft RIPE document summarizing the observations made
	regarding AAAA resolution problems. Circulate to the list,
	initiate discussion what to, i.e. whom to approach with the list
	of errors/problems seen.

I checked with Peter, and he says the documents are pretty freeform,
so I've written a few paragraphs, included below.

	David



This document is a short description of problems with certain DNS
systems that have come to light with the deployment of IPv6 enabled
software.

---

One of the services that DNS provides is a facility for mapping
host names to IPv4 addresses. This is probably the most common used
service that DNS provides, and is achieved requesting a record of
type "A" for the host name. Records of type A can only store an
IPv4 address, and so with the introduction of IPv6, a new record
type, AAAA has been introduced. It is becoming increasingly common
for software to first issue a request of type AAAA, and if no record
of that type is found then to issue a request for a record of type
A.

A request for a record of type AAAA causes no problems for most DNS
servers, however some DNS servers have been found that have problems
answering queries not of type A. The technical details of these
problems are explained in the IETF draft document
draft-ietf-dnsop-misbehavior-against-aaaa-01.txt.  In 2004, about
0.5--1% of name servers seem to have to have a problem of this
nature.  The end result of these issues is that connecting to a
site using a problematic name server may be impossible, intermittent
or significantly delayed.

To prevent introducing more DNS servers with such issues, testing
of new DNS equipment should include checking that the response for
records is in accordance with the RFCs. As DNS load balancing
software has often fallen foul of these problems, particular care
should be taken in testing and validating such systems.

The fact that problematic nameservers exist is in itself a problem.
Where these issues cause direct inconvenience, the maintainers of
the server and the maintainers of the DNS data should be notified
to allow a normal service to be restored. However, often it is
difficult for end users to identify the source of these problems,
(for example, where an image embedded in a web page being served
from a host with a problem hostname).

It is also possible to automatically produce lists of names and
nameservers that exhibit these problems. Clearly it is possible to
automatically mail hostmaters or to publish "hall of shame" lists
based on such data. It is unclear if such actions would achieve
any useful effect, as service maintainers are usually primarily
concerned about complaints directly from paying users!