Re: Adoption Call for <draft-troan-6man-universal-ra-option>

[Brian E Carpenter <[e-mail]>]

On 23-Sep-21 01:49, Philip Homburg wrote:
>> It does exactly what it wa
>> s designed
>> to do, what we called "the dentist's office scenario" in the early days of IPn
>> g design, actually modelled mainly on Appletalk. You can hook a few IPv6 boxes
>> together on a wire and they will start talking to each other using SLAAC and 
>> link-local addresses. Add a router with a prefix and they will start talking t
>> o the world using SLAAC and RA. DHCPv6 is completely unnecessary until the net
>> work reaches a certain level of complexity.
> 
> I'm confused about the relevance of the "the dentist's office scenario".
> 
> As far as I know, the "the dentist's office scenario" is when there is no
> router of any kind on a subnet.

Yes, I think that was the world view in ~1994 when this conversation started.
I was thinking of SLAAC, not SLAAC+RA. SLAAC starts with link-local addresses.
Certainly, a modern version of "dentist's office" is more like a homenet with
several in-house routers. RA is what you get out of the box when you install
an IPv6 router. Then you need ULAs unless you have an active ISP.

Just to be clear, we defined IPv6 in such a way that it doesn't depend on
having an active ISP or any kind of centralised top-down configuration.
That's something we need to keep; we aren't here to support any 
particular business model such as an ISP-based Internet. (The very
concept of "CPE" assumes that business model.)

Of course, we also need the ability to add either top-down configuration via
something like DHCP, or automatic self-configuration. The latter could make
DHCP redundant. There's nothing magic about DHCP; it's just an overlay on
the basic IPv6 mechanisms if you want centralised top-down configuration.
If you don't want that, you don't want DHCP.

> Both RA and DHCP are equally irrelevant.
> That scenario seems completely unrelated to this discussion. Basically the
> support we have for the "the dentist's office scenario" is that hosts
> automatically configure a link-local address. Nothing more nothing less.
> 
> These days, most devices communiate over wifi. And it is hard to find
> a wifi access point in a dentist's office that doesn't have a built-in router.
> 
> As the current IPv4 network shows, even the smallest networks work fine 
> with DHCP. DHCP in modern CPEs is completely automatic. So the notion
> that a small network would need something like RA is rather weird.

I remind you that we did the basic IPv6 design, including RA, before DHCP
was a thing. (Strictly speaking, it was an emerging technology.)
DHCPv6 is an add-on.

> Where RA goes beyond DHCP is in supporting multiple default routers. Which
> is no longer a small, simple network. And in my experience, having multiple
> routers announcing their own prefixes, creates interesting corner cases.

It does. Hence RFC8028 and PVDs.

   Brian