[Kea-users] Problems trying to implement RFC 8925 (v6-only-preferred)

[Dan Oachs]

I'm confused.  What is the issue with Kea offering v6 only clients an ipv4
address?  The client will not accept the ipv4 address and kea will not
reserve that IP address for them.  The end result is a drastic reduction in
ipv4 pool usage.  At least, that's how it is working for me.

Thanks,
  Dan Oachs


On Sun, Jul 30, 2023 at 2:44 PM Brian Candler <b.candler at pobox.com> wrote:

> On 30/07/2023 14:28, Darren Ankney wrote:
> > I have not tested this, but you could use the 'v6-only-preferred'
> > setting in the subnet (see:
> >
> https://kea.readthedocs.io/en/kea-2.4.0/arm/dhcp4-srv.html#ipv6-only-preferred-networks
> ).
>
> As the config I included in my original mail shows, I'm already using
> that option.  Yes it works.  But I still end up *offering* clients an
> IPv4 address from the pool, even those which request the
> v6-only-preferred option and will actually not request the offered
> address; and RFC 8925 says the server should set yiaddr 0.0.0.0 in this
> situation.
>
> > If I'm understanding what you are saying ... DON'T allocate v4 to
> > clients who DON'T send v6 only option?  Won't that result in a bunch
> > of clients with no IP at all?
>
> No, because those clients will still be able to get an IPv6 address (via
> either SLAAC or DHCPv6, depending on what I set up on the network)
>
> > Kea does not appear to offer native support for RFC 2563.  I must not
> > be understanding what you are saying.  You also want the clients that
> > didn't receive any ip address (v4 or v6) to not auto-configure a
> > 169.254 address?
>
> Correct. Clients which don't understand RFC 8925 will still try to
> obtain an IPv4 address.  However, if they support RFC 2563 then I can
> detect this, and use this option to control whether or not they assign a
> link-local IPv4 address.  Again: if I'm not offering them a real IPv4
> address, then the RFC says the yiaddr should be 0.0.0.0.
>
> Clients which don't implement either RFC 2563 or RFC 8925, I don't want
> to respond to.  If they choose to assign a link-local IPv4 address,
> that's up to them.
>
> Regards,
>
> Brian.
>
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