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

[Jen Linkova <[e-mail]>]

On Sat, Dec 7, 2019 at 1:59 AM Bernie Volz (volz) <[e-mail]> wrote:
> I agree with Lorenzo. Keep it simple (see previous email that there really should be no work on the DHCP servers to support this capability).
>
> Yes, you could reserve an address, but I don’t see that as required. Note that I had suggested this to the authors before the draft was published as an optimization; I don’t think it should be the norm. And with many servers, you could probably just do this via configuration (i.e., if PRL contains “IPv6-Only” option, override the client identity with a fixed unique name, add a fixed address / reservation for that unique name).

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) ;)

> From: v6ops <[e-mail]> On Behalf Of Lorenzo Colitti
> Sent: Friday, December 6, 2019 2:21 AM
> To: Jen Linkova <[e-mail]>; Tomek Mrugalski <[e-mail]>
> Cc: V6 Ops List <[e-mail]>; [e-mail]; [e-mail]; Michael Richardson <[e-mail]>
> Subject: Re: [v6ops] [dhcwg] IPv6-Only Preferred DHCPv4 option
>
>
>
> On Fri, Dec 6, 2019 at 4:14 PM Jen Linkova <[e-mail]> wrote:
>
> "If the pool is explicitly configured with a dedicated IPv4
>    address to be returned to IPv6-only capable clients the server MUST
>    specify that address as the client's network address and MUST NOT
>    verify its uniqueness.
>
>
>
> That seems difficult to implement on the server. Why not just return a normal OFFER from the pool? That way, if something unexpected happens and the client sends a DHCPREQUEST for it, the server can hand it out as normal.
>
>
>
> The alternative is risky. If the server uses a bogus OFFER value, and some client requests it and the server hands it out, that creates the possibility for misconfiguration or bugs to create really bad outcomes where multiple hosts have the same IP address, or some things on the network (e.g., snooping switches) think that multiple hosts have the same IP address. +Tomek Mrugalski any thoughts on whether this can be implemented easily and reliably on the server side?



-- 
SY, Jen Linkova aka Furry