Re: [dhcwg] [v6ops] Fwd: New Version Notification for draft-link-dhc-v6only-01.txt

[Roy Marples <[e-mail]>]

On 13/12/2019 01:13, Lorenzo Colitti wrote:
> I really don't see why returning a fake address is preferable.

Please.

All documentation refers to the 0.0.0.0 address as UNSPECIFIED.
It's not fake, it's just all zeros.

UNSPECIFIED means just that. You cannot put ANY specification on it 
otherwise it would not be UNSPECIFIED.

> A real 
> address is easier for many servers to return, and is more compatible 
> with middleboxes.

We've already agreed that middleboxes HAVE to accept yiaddr unspecified 
thanks to RFC2563.

> It also has the advantage that if a client changes its 
> mind (maybe it has in the meantime found out that there is no IPv6 on 
> the link?) it can request it and get it - and again, this all works 
> today because returning real addresses is, in general, what DHCP does. :-)

If a client changes it mind it can renew out of bounds and omit the new 
option. It can say RENEW 1.2.3.4 and the server can OFFER 0.0.0.0.
In just the same way today that a client can request 10.0.0.1 and the 
server will OFFER 192.168.0.1.

DHCP already caters for this :)

And this is also a bone of contention - we should not be allowing a 
state dependant on another.
It's bad enough a hostname from DHCP saying foo and from DHCPv6 saying bar.
I would hope a sys admin would at least know if they ran NAT64 or not 
which is kinda the purpose of this RFC.

> What is the advantage of returning a fake address?

It's not fake. IT'S AN UNSPECIFIED ADDRESS.
CAPS for emphasis because it's like IMPORTANT.
The unspecified address is a real address for both IPv4 and IPv6.

Let me put it another way.

It's perfectly possible for a DHCP server to supply non zero addresses 
to all clients that are unreachable to anyone other than the host they 
are destined for.

How is this different from returning the unspecified address? For all 
intents and purposes, it's just as unreachable.

The address is neither fake, nor invalid - it's just unspecified.
Which is perfect to match this new RFC.

Roy