Why used DHCPv6 when RA has RDNSS and DNSSL?

[Gert Doering]

Hi,

On Thu, Apr 02, 2020 at 05:24:34AM -0300, Fernando Gont wrote:
> > As far as I understand, the official IETF recommendation for "how to
> > run a home with multiple subnets" is "homenet / HNCP" now, which distributes
> > individual /64s via HNCP, not whole prefixes via DHCPv6-PD.
> I haven't been following homenet, to be honest. Is it widely implemented?

Not at all.  IETF killed it nicely, by entering a quabbeling contest
at the crucial "it should be hit vendor implementations *now*" phase -
so after the standards were finally done, all plastic box vendors had
IPv6 implementations in their CPEs and nobody cared about homenet anymore.

(Also, one of the nicest aspects of homenet is "dual ISP multihoming", which
surprisingly ISPs seem to have no interesting in paying their CPE vendors
to implement...  also, still not as nice as one might think due to source 
address selection / source address *failover*)


Picking on just a few bits of your reply (because I am not disagreeing
with most)

[..]
> And the desire to delegate prefixes is also a bit at odds with the 
> strict definition of /64 subnets which end up using a huge address space 
> with a very low host density.

Yes.  If we do away with /64s, and permit hosts to request a, like, /96,
via DHCP-PD, setting this all up would be much much easier - routers
could have a /64 on the LAN, and a second /64 for "as many /96s as you
could possible sustain" - or even "carved out of the /64" (if DHCPv6-IA_NA
is used and the router knows what is free).

Of course this would break *inside* the machine now, when you setup
a "virtual network segment" with said /96, and your android VM refuses
to do DHCPv6-IA_NA on it (and SLAAC doesn't work due to "not /64").


> > Corporate ISP-to-customer delegates a /48, so theoretically, there are
> > "enough /56s in there to do lots of PD delegation to next-level routers" -
> > but in practice, a /48 is supposed to be sufficient for a good-sized
> > office building with *lots* of internal structure, and as soon as you
> > have lots of internal network segments, you have no liberty to just give
> > out random /56s here and there anymore.
> 
> But, in that case, I'm not sure you'd want *dynamic* leases.

Well, as for classic DHCPv6, "it depends".  Most folks are totally happy
with a dynamic endpoint, because they do not need to sustain sessions
across a "change network" event.

Some will want static leases, that follow them around in the building.

But what when they roam to LTE in between?


[..]
> Just curious: what would be the use case of /64 per host (besides trying 
> to limit number of entries in the NC, etc.)?

I let the proponents of DHCPv6-PD-to-the-host answer that - so far I haven't
heard "smaller than /64" proposed anywhere.

Gert Doering
        -- NetMaster
-- 
have you enabled IPv6 on something today...?

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