Re: [v6ops] RFC7084 - absence of req of prefix presence in PIO on LAN?

On Thu, 14 Nov 2019, 06:39 Brian E Carpenter, <brian.e.carpenter@gmail.com>
wrote:

> On 14-Nov-19 03:16, Timothy Winters wrote:
> > Hi Alex,
> >
> > On Wed, Nov 13, 2019 at 2:54 AM Alexandre Petrescu <
> alexandre.petrescu@gmail.com <mailto:alexandre.petrescu@gmail.com>> wrote:
> >
> >>     Hi, v6opsers,
> >>
> >>     While reading through RFC7084 I couldnt find a place where the CE
> Router is mandated to put a prefix in the PIO, even though there is a
> (strange?) requirement to use RIO.
> >>
> >>     I would like to ask:
> >>
> >>     - which existing particular requirement the author assumes to be
> putting a derived /64 in the PIO in the RA?
> >
> > The placing of the prefixes in the PIO from the IA_PD was originally
> located in RFC 3633, so it's not covered in 7084.
>
> More to the point of Alex's question, 7084 says:
>
> >>> The IPv6 CE router MUST support router behavior according to
> >>> Neighbor Discovery for IPv6 [RFC4861].
>
> which therefore requires properly formed PIOs.
>
> >>
> >>     - what does it mean 'An IPv6 CE router MUST advertise itself as a
> router for the delegated prefix(es) [...] using the "Route Information
> Option" specified in Section 2.3 of [RFC4191].'?  (I am asking because I
> suspect this requirement is wrong: the CE Router must certainly not use RIO
> with these prefixes).
>
> Why is that wrong? It is under "LAN requirements:" and seems to mean
> exactly what Alex says next:
>

I'm pretty sure using RIOs was to work around this:

   ULA-5:  An IPv6 CE router MUST NOT advertise itself as a default
           router with a Router Lifetime greater than zero whenever all
           of its configured and delegated prefixes are ULA prefixes

If hosts don't have a default router because of that, then they need to
have other sourced knowledge of the site's ULA prefixes reachable via the
router.

I don't agree with that ULA-5 requirement. The router lifetime in an RA is
a statement of the router's default router status on the link the RA is
sent on, not for the whole site.

It would be fine for hosts to default to a CE for a ULA only site. If they
try to send to somewhere else (e.g. a GUA DA they've somehow acquired), the
DA route lookup would fail in the CE's default free route table, and the CE
would generate an ICMPv6 Destination Unreachable.

There was a fault with a CPE I looked at back in 2010 where it wouldn't
send ICMPv6 Destination Unreachables in this scenario. That caused long
IPv6 timeouts. Other CPE would send an ICMPv6 Destination Unreachable, and
the browser would switch to IPv4 almost immediately.

HappyEyeballs was effectively motivated by a bug, although it does cover
off ICMPv6 Destination Unreachables not being sent because of ICMPv6 send
rate limits, per RFC 4443, 2.4, (f).

> >> CE Routers should place the RIO in the RAs on the LAN interface to have
> Host route traffic for those prefixes to that Router if they have
> multi-homed
>
> (Although, not surprisingly, I would like to see RFC8028 mandated too.)
>
> Regards
>     Brian
> >>
> >>     Alex
> >
> > Regards,
> > Tim
>
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