Subject: RE: dns discovery for agenda? [Re: chairs and charter]

From: [email-masked]
Date: Wed, 19 Mar 2003 07:17:42 +0200

Hi all,

> > With all due respect, I think this is short sighted. Today you almost
> > cannot buy a DSL router for home use that doesn't have an integrated
> > DHCP server, among all kinds of other strange stuff. To make a future
> > equivalents of such devices also talk DHCPv6 is clearly possible.
> 
> Sure.  But that's then still a lot of DHCP code for just DNS discovery
> (if DNS discovery is all that is required of the DHCPv6 server, and the
> node doesn't need other DHCPv6 options).

My major concern about DHCP for DNS discovery will be deployment of DHCPv6
servers.  How long will it be before the IETF deploys DHCPv6 at meetings?
Already, at a number of IETF meetings, I have had IPv6 addresses, but
because of DHCP problems (client and server problems), I have been
unable to get IPv4 addresses & DNS server addresses.  

It breaks down to this, if I want to deploy IPv6 nodes, can I count on DHCPv6
servers being out in the networks?  I am not debating or commenting on 
the DHCPv6 at all, what I am saying is that in the absense of working DHCPv6 
servers, I would like a fall-back.

If we have statefull address autoconfig & stateful address autoconfig, I think
having an additional mechanism for getting DNS server addresses is not a 
bad thing.  At the transport layer, we have UDP, UDP-lite, DCCP, TCP, SCTP ...
to transfer packets.  Having multiple ways to do something is a reasonable
solution.

John

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From: Erik Nordmark <[email-masked]>
Date: Wed, 19 Mar 2003 06:19:34 +0100 (CET)

> If we have statefull address autoconfig & stateful address autoconfig, I
> think having an additional mechanism for getting DNS server addresses is not
> a  bad thing.  At the transport layer, we have UDP, UDP-lite, DCCP, TCP,
> SCTP ... to transfer packets.  Having multiple ways to do something is a
> reasonable solution.

Two issues with multiple methods to configure the same thing that
hasn't been brought up are:
 - potential impact on time to discover
	Since each router advertisement doesn't need to contain all
	options will a host need to listen for RAs for some time
	before it decides it to DHCPv6 to find the info?
 - conflicting information
	A host might use DHCPv6 for other reasons/other information.
	What should it do if the RAs and the DHCPv6 reply contains
	different DNS information?
	What if different RAs received on the same interface contain
	different DNS information?

  Erik

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From: Brian Haberman <[email-masked]>
Date: Wed, 19 Mar 2003 11:52:41 -0500

Erik,

> 	different DNS information?

A few points on your last issue.  The NDP spec does state that if
two routers detect conflicting info in the RAs that they should
log a warning.

That approach will help the operator with fixing the conflicting
info, but doesn't benefit the nodes that are receiving that info.
For them, perhaps what we should do is state that they should
honor the RA coming from the router with the lowest IPv6 address.

By doing that, operators can assign some level of priority to
their RAs.

Regards,
Brian

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From: Ralph Droms <[email-masked]>
Date: Wed, 19 Mar 2003 12:43:37 -0500

Regarding conflicting DNS information - in theory, it shouldn't matter if 
there is conflicting information about DNS servers, as the host would 
receive the same response to a DNS query send to any of the DNS servers.

I am DNS-naive and my comment about "in theory" may well be wrong, either 
in theory or in practice.  So, does the choice of DNS server really make a 
difference or can a host simply choose from the union of all  of the lists 
of DNS servers it receives?

- Ralph

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From: Mika Liljeberg <[email-masked]>
Date: 19 Mar 2003 19:52:07 +0200

> 	different DNS information?

If they all work, what's the problem?

	MikaL

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From: Stig Venaas <[email-masked]>
Date: Wed, 19 Mar 2003 19:05:30 +0100

> 	different DNS information?

I this problem also might arise for dual-stack host using DHCP.
Should it query DHCPv6 and/or DHCP? Should it fall back to one
if the other fails?

Stig

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From: Erik Nordmark <[email-masked]>
Date: Wed, 19 Mar 2003 21:47:33 +0100 (CET)

> honor the RA coming from the router with the lowest IPv6 address.

Yes, this is one way to resolve the conflict.

But my point was really trying to be at a higher level:
When there are different ways to config the
same thing one needs to *think* about conflicts and conflict resolution.
The answer might be some scheme for resolving the conflict, or
that there isn't such a need for the particular thing that is
configured.

  Erik

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From: Erik Nordmark <[email-masked]>
Date: Wed, 19 Mar 2003 22:20:40 +0100 (CET)

> Should it query DHCPv6 and/or DHCP? Should it fall back to one

Yes for the conflicting information question.
But I think the issue whether to use DHCPv4 or DHCPv6 are driven by external
events. Once it has decided to use both they might present different
information for different things.

But I think the issue whether DHCPv6 will provide IPv4 addresses for DNS
servers is relevant to this issue. I don't recall what the resolution was
for that issue.

  Erik