Subject: RE: Proposed M&O bits text for RFC2461bis

From: "Durand, Alain" <[email-masked]>
Date: Tue, 21 Mar 2006 14:51:38 -0500

>     M :
>         1-bit "Managed address configuration" flag.  When set, it
indicates
>         that addresses are available via Dynamic Host Configuration
Protocol
>         [DHCPv6], including addresses that were not configured via
stateless
>         address autoconfiguration.

I'm not sure I understand the last part of the sentence...
Does it means that addresses configured via stateless address
autoconfiguration
are -also- availabe via DHCP?

>          Clients SHOULD use DHC to obtain addresses

This is the core of the suggested change going from what was the
equivalent of a MAY
to a SHOULD... What is the rationale for that change?

>         (and associated configuration information) as described in
[ADDRCONF].
>         Note that when the M bit is set, the setting of the O bit is
>         irrelevant, since the DHC server will return "other"
configuration
>         information together with addresses.

The texts says nothing about what the client is supposed to do when the
bit is not set.
(same comment with O)

   - Alain.

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From: Thomas Narten <[email-masked]>
Date: Tue, 21 Mar 2006 19:48:03 -0600

"Durand, Alain" <[email-masked]> writes:

> >     M : 1-bit "Managed address configuration" flag.  When set, it
> >     indicates that addresses are available via Dynamic Host
> >     Configuration Protocol [DHCPv6], including addresses that were
> >     not configured via stateless address autoconfiguration.

> I'm not sure I understand the last part of the sentence...  Does it
> means that addresses configured via stateless address
> autoconfiguration are -also- availabe via DHCP?

No, it means that if you don't invoke DHC to get addresses, you won't
be getting all the addresses the network is telling you it thinks you
need. That is, DHC is providing addresses that are (presumably) not
available via stateless addrconf, hence you should use DHC to get
them.

I agree the wording could be better, e.g., 

    M : 1-bit "Managed address configuration" flag.  When set, it
        indicates that addresses are available via Dynamic Host
        Configuration Protocol [DHCPv6], including addresses that are
        likely not available via stateless address autoconfiguration.

> equivalent of a MAY to a SHOULD... What is the rationale for that
> change?

Per my comment above, if you don't invoke DHC, you won't get all the
addresses the network is configured to be giving you. Hence, you
SHOULD invoke DHC to get them.

> The texts says nothing about what the client is supposed to do when the

Actually, the text concludes with:

       Note that if M and O are not set, clients SHOULD NOT not
       request any information with DHC.

Perhaps that should be changed to

       Note that if neither M nor O are set, clients SHOULD NOT not
       request any information with DHC.

Thomas

---

From: Fred Baker <[email-masked]>
Date: Tue, 21 Mar 2006 23:58:00 -0600

On Mar 21, 2006, at 7:48 PM, Thomas Narten wrote:
>> I'm not sure I understand the last part of the sentence...  Does  
>> it means that addresses configured via stateless address  
> No, it means that if you don't invoke DHC to get addresses, you  
> won't be getting all the addresses the network is telling you it  
> thinks you need. That is, DHC is providing addresses that are  
> (presumably) not available via stateless addrconf, hence you should  
> use DHC to get them.

More to the point, if you are in a shop that has decided to allocate  
addresses by DHCP, calculating an address via autoconfiguration is  
the wrong answer. Not because it is politically correct or otherwise,  
but because it is the policy of the network, and the IETF doesn't get  
to decide that.

BTW, there is a lot of host configuration that is communicated via  
DHCP that isn't the node address and isn't covered by  
autoconfiguration. Whether or not I agree that address assignment by  
DHCP is the right answer, not supporting the other is cutting one's  
nose off to spite one's face.

---

From: "Christian Huitema" <[email-masked]>
Date: Tue, 21 Mar 2006 22:21:53 -0800

> but because it is the policy of the network, and the IETF doesn't get

We went through that before. The proper way for a network to indicate
that nodes should not use auto-conf is simply to not advertise prefixes
with the auto-conf bit set. If the auto-conf bit is set, then hosts may
obviously auto-configure addresses.

In fact, it would be good to be a bit more specific about the expected
behavior when both auto-conf and DHCP are allowed (both M and A bits).
Is the host expected to auto-allocate an address and then confirm it
through DHCP? Does it use the union of DHCP and auto-config? What about
privacy addresses?

-- Christian Huitema

m ([157.54.69.150]) by mail3.microsoft.com
	with Microsoft SMTPSVC(6.0.3790.2499); 
	Tue, 21 Mar 2006 22:22:11 -0800
Content-class: urn:content-classes:message
Date: Tue, 21 Mar 2006 22:21:53 -0800
From: "Christian Huitema" <[email-masked]>
To: "Fred Baker" <[email-masked]>,
	"Thomas Narten" <[email-masked]>
Cc: "Durand, Alain" <[email-masked]>,
	IPv6 Mailing List <[email-masked]>, Bob Hinden <[email-masked]>
Subject: RE: Proposed M&O bits text for RFC2461bis 

> but because it is the policy of the network, and the IETF doesn't get

We went through that before. The proper way for a network to indicate
that nodes should not use auto-conf is simply to not advertise prefixes
with the auto-conf bit set. If the auto-conf bit is set, then hosts may
obviously auto-configure addresses.

In fact, it would be good to be a bit more specific about the expected
behavior when both auto-conf and DHCP are allowed (both M and A bits).
Is the host expected to auto-allocate an address and then confirm it
through DHCP? Does it use the union of DHCP and auto-config? What about
privacy addresses?

-- Christian Huitema

---

From: Ralph Droms <[email-masked]>
Date: Wed, 22 Mar 2006 01:27:54 -0500

There is very little to be said about auto-conf/DHCPv6 interaction:

DHCPv6 and stateless address auto-configuration and the addresses assigned
through each process are independent of each other.  A node may run either,
both or neither DHCPv6 and SLAAC.

How are privacy addresses an issue?

- Ralph

---

From: Erik Nordmark <[email-masked]>
Date: Wed, 22 Mar 2006 08:19:18 -0800

> SHOULD invoke DHC to get them.

I think making that a SHOULD is premature and too strong, since we 
haven't explored what the desirable behaviors are when both M and A bits 
are set.
(When M is set and no prefix has A, then using DHCP is a no-brainer.)

I can imagine that a host wants to have the option to have local policy 
to handle the case when both M and A bits are set, but there is nothing 
in the "SHOULD" that allows for local policy control.

If we want to work out more details in this space, I suspect we need to 
start with understanding why some operator would set both M and A bits. 
But I think we can defer that discussion until we have more deployment 
experience.

    Erik