Re: IPv6 Deployment for the LAN

[Nathan Ward <nanog () daork net>]

On 18/10/2009, at 9:03 PM, Andy Davidson wrote:

> I don't know the history of the process that led to DHCPv6 ending up  
> crippled, and I have to admit that it's not clear how I signal this  
> and to whom, but for the avoidance of doubt: this operator would  
> like his tools back please.  Support default-routing options for  
> DHCPv6 !

I think what you really want is an on-link prefix option in DHCPv6. Or  
at least, you'd need that as well as a default router option.

As I've said before, RA does not mean SLAAC. DO NOT use the two words  
interchangeably.

We have two address configuration mechanisms, RA is the transport for  
one (SLAAC) and is the hint to use another (DHCPv6 stateful).
The use of RA does NOT require the use of either mechanism.
Without RA, we don't know which to use, without manual configuration.  
I for one don't want to have to fool around every time I move to a new  
network, and I'm a tech guy.

Can we put this in to a FAQ somewhere, I write this in almost every  
IPv6 thread that comes up on NANOG.



The reason Ray's perceived problem exists is that when using DHCPv6  
stateful for address configuration, you should also include the prefix  
in an RA message. This is because DHCPv6 doesn't give out prefix  
lengths, it only gives out addresses.

There is an option (the A bit) with each prefix in an RA message,  
which says whether this prefix can be used for SLAAC or not (1 =  
SLAAC). Ray's perception (fear?) is that there are some  
implementations that will ignore the contents of this bit, and use the  
prefix for SLAAC regardless.

I'm interested to see if these implementations actually exist, I  
haven't come across any myself or heard of any - but I've not been  
looking.


Anyway, start here for a discussion of prefix lengths in DHCPv6:
http://www.ietf.org/mail-archive/web/dhcwg/current/msg07412.html

--
Nathan Ward