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

[Lorenzo Colitti <[e-mail]>]

On Mon, Dec 9, 2019 at 1:30 PM Jen Linkova <[e-mail]> wrote:

> Practically speaking I'd prefer to minimize the risk.
> While do not know the probability of a smart infrastructure device
> getting an allergic reaction to abnormal DHCP packet, the potential
> impact is quite high.
>

+1


> I'm not sure what's the impact of returning an address (ex. for making
> that address unavailable for a short period of time)?
>

The only downside that I can think of is that if you have a thundering herd
of devices that come online all at the same time (e.g., power loss and
site-wide reboot), the offers handed to the v6only-capable devices, in the
brief time they are allocated, can exhaust the pool such that
v6only-incapable devices cannot immediately get an address. However, the
server can mitigate that in two ways:

   1. When issuing an offer, don't reserve the address, or reserve it for a
   very short time.
   2. When issuing an offer to a v6only-capable device, don't reserve the
   address. If the v6only-capable device then comes back and sends a request
   (which it shouldn't, unless something very strange happens), then the
   address may be in use by a v6only-incapable device. In that case, the
   v6only-capable device will get a nak and can go back to discover.