Re: Multiple addresses [was Node Requirements: Elevating DHCPv6 from MAY to SHOULD]

[Tim Chown <[e-mail]>]

On 31 May 2011, at 03:38, Fred Baker wrote:
> 
> I would expect, however, that the use of DHCP is something configured on the system in question, just like it is in IPv4. Not that there is an auto-configure option in IPv4 - the other alternative is manual configuration, and most systems come with DHCP configured as the default. IPv6 systems come, at least today, with SLAAC as the default. So there is a requirement to configure DHCPv6, at least from that perspective. That said, SLAAC ain't gonna happen in the absence of RAs, and you can disable RAs on the router. So if an interface comes up and no RA is forthcoming, I could imagine the thing probing with a DHCPv6 request.

But then it can't get a default router configuration by DHCPv6?

It's interesting that my 18(?) month old HP Laserjet n model has IPv6 support, and even being that old can be configured to 

a) just autoconfigure
b) use DHCPv6 when the M bit is set in the RA
c) use DHCPv6 when stateless autoconfig fails
d) always use DHCPv6
or
e) use a manually-configured IPv6 address. 

If you're interested in how that appears via the HP web config screen, see a screenshot at http://users.ecs.soton.ac.uk/tjc/ietf/hplaserjet-example.png

I think, but am not sure, that the screenshot shows the default configuration.  While there is no privacy addressing in this example, that could be an additional option, though it makes little sense for such a device.

To me, if you want to run DHCPv6, you set the RA M bit, and it's then down to hosts to choose to honour that.  But if you don't have management control of any device, unless you put additional measures in place, the host can always be configured with a different/additional address to that offered by DHCPv6. 

Tim