Re: [v6ops] [dhcwg] IPv6-Only Preferred DHCPv4 option

[Lorenzo Colitti <[e-mail]>]

On Mon, Dec 9, 2019 at 9:54 AM Jen Linkova <[e-mail]> wrote:

> I'm fine with it. I'll remove the reference to a dedicated address to
> return.
> So just to summarise the discussion: we have a number of options on the
> table:
> a) let server just return *an* address from the pool, assuming that as
> the host would not accept the offer anyway, the address will be made
> available again soon;
>    pros:
>       --- no changes on the server side;
>       --- it would look normal to smart middle boxes
>    cons:
>       --- might lead to higher pool utilisation
> b) return some bogus address (0.0.0.0 or smth else)
>     pros:
>        --- client would not be able to assign it (hmm..theoretically)
>       --- optimized pool usage
>    cons:
>       --- requires changes on the server
>       --- might trigger unexpected behaviour on smart middle boxes
> (==> slowing down the adoption)
>
> c) do not offer anything, do smth esle instead (what exactly?)
>
> After writing it down like that I do agree that we shall probably choose
> a) ;)
>

I would change b) "return 0.0.0.0" and add:

d) configure a specific address from the pool for all IPv6-only-capable
clients
    pros:
       --- most efficiently preserves IPv4 addresses. Always works even if
all clients ask for an address at the same time.
   cons:
      --- requires changes on the server
      --- client cannot actually get the address, so if it sends a request,
things won't go well.

In that sense I think b) is a non-starter, and I don't think c) is feasible
either: we do need to return something to the client, otherwise it can't
know that IPv6-only will work, and I don't think there's anything other
than OFFER that the server respond with (I don't think NAK is typically
sent in response to DISCOVER).

So I think we're down to a) offer a regular address from the pool, and d)
offer a bogus address. The draft attempts to do both right now. I wonder if
we could leave d) in the text, but make it clear that it's just a possible
optimization?