DHCP6 and RA,M=1,PIO,A=0

[james woodyatt <jhw@apple.com>]

On Nov 20, 2008, at 17:22, Fred Baker wrote:
> On Nov 20, 2008, at 10:40 AM, Rémi Denis-Courmont wrote:
> > On Thursday 20 November 2008 18:14:41 Fred Baker, you wrote:
> > > So I understand your comment as less than supportive of the  
> > > document. In what ways do you believe it needs to change?
> >
> > I am just dubious about the DHCPv6 solution. I think it needs to be  
> > better studied, so that we understand what (if anything) it would  
> > solve.
>
> I think operational folks can tell you pretty quickly what it  
> solves. It enables an operator to specify an address for an end  
> system as opposed to letting the end system dream one up.

Strictly speaking, it enables an operator to translate the MAC address  
of an endpoint interface into its assigned IPv6 interface address.   
It's ICMPv6 RA that specifies that an endpoint interface isn't allowed  
to dream up its own address.  I mention this distinction because it's  
important to the point I make below.

> If the argument is "I just think people should be using  
> autoconfiguration", I have no problem with autoconfiguration, but I  
> know network managers that do. "I don't like it" is no where near as  
> useful a comment as "I have identified a problem".

Network managers who think it's important to be able to control the  
assignment of IPv6 interface addresses to physical interfaces often  
make the mistake of assuming that MAC addresses are fixed on hardware  
manufacturing lines and cannot be changed in user software.

I'm here to say that's a painfully stupid mistake.

Whatever could possibly be the point of disabling address self- 
assignment on a subnet when the network management system cannot be  
certain either A) that the device presenting a specific MAC address to  
the network is the same device that presented it last time, or B) that  
the device presenting you a particular MAC address this time will ever  
present that MAC address to you again in the future?

If you deploy a network management system that insist on pairing a MAC  
address with a specific managed entity [especially, a *billable*  
entity], then you will be forcing people like me to make MAC address  
cloning even easier to do than it already is... (and don't think I'm  
at a loss for ideas about how to do that).

Is encouraging MAC address cloning what we are trying to do here?   
Because I have a hard time believing it.


--
james woodyatt <jhw@apple.com>
member of technical staff, communications engineering