Subject: DNS resolution hints

From: "Art Shelest" <[email-masked]>
Date: Mon, 22 Apr 2002 17:33:56 -0700

Hi: 

Hopefully someone has a suggestion for the problem I'm having.

Background:
In the Dynamic DNS environment, an IPv4/IPv6 dual host registers two or
more DNS records with the same name: A record for the IPv4 and AAAA
record for the IPv6.

Problem:
When testing or troubleshooting applications, it's useful to isolate a
single protocol. With a hostname resolving to both A and AAAA, there's
no telling which address and which protocol will be used for
communication.

Existing solutions and their drawbacks:
- edit the hostname file. Beyond the skill and/or privilege level of
many testers or troubleshooters.
- set up own DNS server. Requires decent understanding of DNS, also see
above.
- use literal addresses. Not all applications permit use of literals.
- use a utility to register AAAA-only or A-only records in the DNS. Tool
no readily accessible for remote (over-the-phone) troubleshooters. May
run against the company network use policy
- have each host register an additional, distinct name that only
resolves to IPv6. Results in additional DNS registration/replication
traffic.

A possible alternative is to permit name resolution hints in the DNS
name that would be processed by the resolver. For example, one could
enter "www.-6.kame.net" and be sure that the application is using IPv6
transport to talk to the server.

In the example above, the resolver would interpret the ".-6" as a
directive to only ask for AAAA record of the www.kame.net.

---
Art Shelest              Tel: (425) 703-5666
Program Manager          Fax: (425) 936-7329
Microsoft Corporation    microsoft.com/ipv6

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---

From: Jim Reid <[email-masked]>
Date: Tue, 23 Apr 2002 01:08:47 -0700

>>>>> "Art" == Art Shelest <[email-masked]> writes:

    Art> Problem: When testing or troubleshooting applications, it's
    Art> useful to isolate a single protocol. With a hostname
    Art> resolving to both A and AAAA, there's no telling which
    Art> address and which protocol will be used for communication.

Surely that's a decision for the application that made the lookup?
This is no different from a query which returns a bunch of IP
addresses because the name being looked up is for a multi-homed host:
which one does the application use? Policy issues like this shouldn't
get "solved" in the DNS. They don't belong there. Presumably the
application could be given selection criteria through something like a
configuration (file) option or environment variable or, since you're
from Redmond, a registry setting.

---

From: "Art Shelest" <[email-masked]>
Date: Tue, 23 Apr 2002 08:56:33 -0700

Jim:

Thank you for pointing out the option that didn't make on the list of
workarounds:

* an application speficic option

Pros: does not require DNS changes.
Cons: needs to be implemented for every application that requires
testing or troubleshooting. Cannot be implemented for apps that do not
call getaddrinfo directly, such as apps using RPC, or any connectivity
library.

This is the solution used by ping, tracert and pathping, currently
implemented in WinXP.
For example, ping -6 www.example.com will only use IPv6 address.

One cannot make this work for Outlook (uses RPC) or IE (uses generic
HTTP system API).

Thanks!

-----Original Message-----
From: Jim Reid [mailto:[email-masked]] 
Sent: Tuesday, April 23, 2002 1:09 AM
To: Art Shelest
Cc: [email-masked]
Subject: Re: DNS resolution hints 

Surely that's a decision for the application that made the lookup? This
is no different from a query which returns a bunch of IP addresses
because the name being looked up is for a multi-homed host: which one
does the application use? Policy issues like this shouldn't get "solved"
in the DNS. They don't belong there. Presumably the application could be
given selection criteria through something like a configuration (file)
option or environment variable or, since you're from Redmond, a registry
setting.

---

From: Danny Mayer <[email-masked]>
Date: Wed, 24 Apr 2002 00:08:07 -0400

>One cannot make this work for Outlook (uses RPC) or IE (uses generic

Since Microsoft owns these applications, there is nothing to prevent you from
modifying the application to check the registry for such a flag or include it
on the command line when it is started. Assuming that Microsoft is going to
be using the SRV records for looking up available services, you should be
able to set up the SRV record to point to either v4 or v6 addresses only.

         Danny