DHCPv6, was: Re: IPv6 Finally gets off the ground

Sun Apr 15 21:42:23 UTC 2007

On 15-apr-2007, at 21:35, Joe Abley wrote:

>> With IPv6, there's of course still manual configuration, but PPP  
>> is out because it can't negotiate IPv6 addresses.

> I've heard you say this a few times now, but I am also told by  
> various people in various places that they have succeeded in  
> getting IPv6 addresses assigned using PPPoE. Colour me confused.

> Does RFC 2472 have some practical limitations in the real world  
> that I haven't noticed? Or is the problem a simple matter of  
> implementation?

With IPv4, PPP IPCP will negotiate a whole bunch of stuff, including  
the addresses of both sides of the link. PPP IP6CP only negotiates a  
32-bit unique token for each side which can then be used to create  
link local addresses.

Two years ago, when I was writing my IPv6 book, I did some testing  
between an Cisco 2500 and a MacOS 10.4 system to see how IPv6 over  
PPP behaves, and the result was that it did work, but there was no  
address assignment from the router to the Mac, not through PPP,  
because it doesn't support it, and not through router advertisements,  
for reasons unknown. Probably someone decided that stateless  
autoconfig on a point to point link didn't make sense.

(Note that the pppd in question is common to both the BSD family and  
Linux.)

I have no idea what's different in the PPP over ethernet setup, but  
it could be many things, such as that the PPP implementations do  
support stateless autoconfig there, or that it's not actual IPv6 over  
PPP but rather IPv6 over IPv4 or over bridged ethernet.