[Snac] Re: Why is an AIL prefix with only the "P" flag set suitable?

[Ted Lemon <[e-mail]>]

On 21 Nov 2025, at 20:29, Michael Richardson <[e-mail]> wrote:
> Ted Lemon <[e-mail]> wrote:
>> Consider the bad home router case. In this case, the home router is in violation of RFC7084:
> 
>> WAA-1:   The IPv6 CE router MUST support Stateless Address
>> Autoconfiguration (SLAAC) [RFC4862].
> 
> Support != enable!
> {I think that I can explicitely turn off SLAAC on OpenWRT, relying on DHCPv6-only}

It's pretty clear that the document assumes that SLAAC will be enabled by default. However, you're right that it doesn't say that explicitly. It does say "The A and L flags' ([RFC4861 <https://www.ietf.org/archive/id/draft-ietf-v6ops-rfc7084bis-04.html#RFC4861>]) settings SHOULD be user configurable." which implies that there is a default.

>> So I think we don't need to address this case, because non-conformant
>> home routers should be out of scope. E.g., a home router MUST NOT
> 
> I think that word non-conformant is incorrect, but I agree that it probably
> should be out-of-scope.

It should be the case that such a router is non-conformant, and I will mention that on the v6ops mailing list.

> ...
>> It's of course possible that the operator of a home router might turn
>> off SLAAC, but in that case you have a managed network. Which brings us
>> to the second case—a misconfigured or deliberately configured managed
>> network.
> 
> Agreed: This might have been done by an incompetent ISP.
> So in this case, we need enough text for an end-user to hit them over the head.

I don't think we can require that the ISP not disable SLAAC, but realistically if they do they are going to get a lot of phone calls. Well, assuming the end user cares about IPv6.

>> If it's deliberately configured this way, then I think it makes sense
>> to follow the operator's intention. Our goal here is not to make every
>> network SNAC-capable, but rather to make sure that when SNAC should
>> work, it does work. In this case, the operator has clearly decided that
>> SNAC shouldn't work for hosts that don't do IA_PA (or possibly
>> IA_NA). I think it's fine for us to not solve this problem.
> 
> +1
> The STUB network could well work via PD (or ULA+NAT64 even), but not interact
> with the AIL.  We should document this limitation clearly then.
> _It's working as intended_

OK. Send text (to github)?