Subject: Response to Dave Thaler regarding server-initiated DHCPv6

From: Ralph Droms <[email-masked]>
Date: Tue, 10 Nov 2009 10:58:30 +0900

In the discussion of IPv6 address selection , Dave Thaler asked me to  
comment on this bullet from slide 10:

* DHCP option
   - Hard to kick policy reconfigure by a server.

Not wanting to contribute to yet another iteration of the RA-vs-DHCP  
debate, I'm responding through the mailing list.  DHCPv6 has an  
explicit mechanism, required by RFC 3315, in which a server can  
asynchronously trigger a DHCPv6 message exchange from the client.

Suresh commented that the router might be a better source of updates  
in some circumstances, when the selection policy is modified by  
changes in the routing infrastructure as propagated by routing  
protocols.  I haven't thought about that scenario and can't comment...

- Ralph

---

From: Arifumi Matsumoto <[email-masked]>
Date: Tue, 10 Nov 2009 11:06:12 +0900

On 2009/11/10, at 10:58, Ralph Droms wrote:

> In the discussion of IPv6 address selection , Dave Thaler asked me  
> to comment on this bullet from slide 10:
>
> * DHCP option

I know there is RECONFIGURE message of DHCPv6,
but it requires secured channel to use it.
So, I described "Hard" here.

Hard means that it cannot be used everywhere the
DHCP is used nwo.

Thanks.

> --------------------------------------------------------------------
> IETF IPv6 working group mailing list
> [email-masked]
> Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6
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---

From: Ralph Droms <[email-masked]>
Date: Tue, 10 Nov 2009 11:14:38 +0900

DHCPv6 Reconfigure can be "secured" using an additional "Reconfigure  
Key" that does not require a shared secret or other pre- 
configuration.  So, the DHCPv6 Reconfigure has essentially no  
overhead.  See section 21.5 of RFC 3315.

- Ralph

On Nov 10, 2009, at 11:06 AM 11/10/09, Arifumi Matsumoto wrote:

>> Not wanting to contribute to yet another iteration of the RA-vs- 
>> DHCP debate, I'm responding through the mailing list.  DHCPv6 has  
>> an explicit mechanism, required by RFC 3315, in which a server can  
>> Suresh commented that the router might be a better source of  
>> updates in some circumstances, when the selection policy is  
>> modified by changes in the routing infrastructure as propagated by  
>> routing protocols.  I haven't thought about that scenario and can't  
>> comment...
>>
>> - Ralph
>>

---

From: Suresh Krishnan <[email-masked]>
Date: Tue, 10 Nov 2009 20:32:24 -0500

Hi Ralph,
   I was just commenting that the addressing policy changes triggered by 
routing changes are best initiated by the router and all the other 
policy changes are best initiated by the DHCP server. I was not 
commenting on the suitability/ease of use of the delivery mechanism(s) 
at all.

Thanks
Suresh

---

From: Ralph Droms <[email-masked]>
Date: Wed, 11 Nov 2009 11:34:27 +0900

OK.

I'll agree that the information about routing changes is available in  
the router.  Whether the router has all the information needed and the  
mechanisms to translate that routing information into policy changes  
for the hosts must also be considered.

- Ralph

On Nov 11, 2009, at 10:32 AM 11/11/09, Suresh Krishnan wrote:

> Hi Ralph,
>  I was just commenting that the addressing policy changes triggered  
> by routing changes are best initiated by the router and all the  
> other policy changes are best initiated by the DHCP server. I was  
> not commenting on the suitability/ease of use of the delivery  
> mechanism(s) at all.
>
> Thanks
> Suresh
>
>> an  explicit mechanism, required by RFC 3315, in which a server  
>> can  asynchronously trigger a DHCPv6 message exchange from the  
>> client.
>> routing  protocols.  I haven't thought about that scenario and  
>> can't comment...
>> - Ralph

---

From: Christopher Morrow <[email-masked]>
Date: Tue, 10 Nov 2009 22:09:21 -0500

On Tue, Nov 10, 2009 at 9:34 PM, Ralph Droms <[email-masked]> wrote:
> OK.
>
> I'll agree that the information about routing changes is available in the
> router.  Whether the router has all the information needed and the
> mechanisms to translate that routing information into policy changes for the
> hosts must also be considered.

surely there will be hybrid scenarios where one side
(router/dhcp-server) or the other have 'better' (more) information. I
think that in the larger scheme, if you provision 'some information'
with dhcp/dhcpv6 you will continue to do that tomorrow.

If there is a network event that triggers host-routing changes you
will have to have coordination between the host & router folks, just
as you do today. If you can have the dhcpv6 server ping it's clients
for an update, so much the better. (even so much better if that comes
in some 'secure' manner!)

-chris

>> routing changes are best initiated by the router and all the other policy
>> changes are best initiated by the DHCP server. I was not commenting on the
>> suitability/ease of use of the delivery mechanism(s) at all.
>>
>> Thanks
>> Suresh
>>
>>>  debate, I'm responding through the mailing list.  DHCPv6 has an  explicit
>>> mechanism, required by RFC 3315, in which a server can  asynchronously
>>> trigger a DHCPv6 message exchange from the client.
>>> Suresh commented that the router might be a better source of updates  in
>>> some circumstances, when the selection policy is modified by  changes in the
>>> routing infrastructure as propagated by routing  protocols.  I haven't
>>> thought about that scenario and can't comment...
>>> - Ralph

---

From: Ralph Droms <[email-masked]>
Date: Wed, 11 Nov 2009 13:13:05 +0900

My point is that "place with better information" and "best place from  
which to deliver information to the host" are not necessarily  
(although likely to be) the same...

- Ralph

On Nov 11, 2009, at 12:09 PM 11/11/09, Christopher Morrow wrote:

>>> policy
>>>> DHCP
>>>> explicit
>>>> updates  in

---

From: Christopher Morrow <[email-masked]>
Date: Tue, 10 Nov 2009 23:55:51 -0500

On Tue, Nov 10, 2009 at 11:13 PM, Ralph Droms <[email-masked]> wrote:
> My point is that "place with better information" and "best place from which
> to deliver information to the host" are not necessarily (although likely to
> be) the same...

agreed. though 'at my house' and 'at my office' are 2 different ends
of that spectrum (I suspect). So I suspect that 'routers' will soon
have 'mostly full' dhcpv6 servers in them...

-Chris

>>>>>  in

---

From: Ralph Droms <[email-masked]>
Date: Wed, 11 Nov 2009 14:04:44 +0900

They don't actually need a full DHCPv6 server.  Support of Information- 
request/Reply/Reconfigure would be sufficient.

- Ralph

On Nov 11, 2009, at 1:55 PM 11/11/09, Christopher Morrow wrote:

>>>> mechanisms to translate that routing information into policy  
>>>> changes for
>>>> the
>>>>> changes are best initiated by the DHCP server. I was not  
>>>>> commenting on
>>>>> the
>>>>>> updates
>>>>>> some circumstances, when the selection policy is modified by   
>>>>>> changes
>>>>>> in the

---

From: Christopher Morrow <[email-masked]>
Date: Wed, 11 Nov 2009 00:07:22 -0500

On Wed, Nov 11, 2009 at 12:04 AM, Ralph Droms <[email-masked]> wrote:
> They don't actually need a full DHCPv6 server.  Support of
> Information-request/Reply/Reconfigure would be sufficient.

I think we're spliting hairs... but eventually someone's going to want
to do all portions of dhcpv6 and NOT do it on a server. Perhaps
looking at this another way, someone's going to recognize that 'root
nfsmount' (or something else odd) is helpful to their cause, and not
want to do that on a dedicated DHCPv6 server, they'll get a vendor to
implement that 'feature' for them.

my point is... it's not one or the other, there will be a myraid of
cases in the middle, which is perfectly fine.

-chris