Re: Understanding IPv6-PD over PPPoE

[Bjørn Mork <bjorn mork no>]

Steve Hill via networkmanager-list <networkmanager-list gnome org>
writes:
> On 16/06/2021 10:12, Beniamino Galvani wrote:
>
> > You are right, RFC 3633 forbids it. However, if I understand correctly
> > this approach is the one mentioned in [1], which refers to an expired
> > IETF draft [2] saying:
>
> RFC 3633 has been obsoleted by RFC 8415, and this MUST NOT does not
> appear to be mentioned in 8415.

Yes, looks like that was dropped.  Probably because it was violated all
the time and this works well in practice :-)

Still doesn't make much sense IMHO. As seen from the delegating router:
Why delegate a prefix for the other end of the link when you can just
assign it directly to your end?

> RFC 8415 references RFC 7084, which says (Emphasis mine):
>
>    WAA-7:   If the IPv6 CE router does not acquire a global IPv6
>             address(es) from either SLAAC or DHCPv6, then it MUST create
>             a global IPv6 address(es) from its delegated prefix(es) and
>             configure those on one of its internal virtual network
>             interfaces, ***unless configured to require a global IPv6
>             address on the WAN interface***.
>
> I think this sort of implies that generating a global IPv6 address for
> the WAN interface from the delegated prefixes is ok?

I believe the intended meaning of the emphasized text is that the CE
address configuraion should fail in this case.

> Its not terribly clear, but in any case the MUST NOT wording seems to
> have gone away.  It feels sensible to me to optionally auto-generate a 
> /128 address for the WAN interface from the delegations if it doesn't
> have an address assigned from elsewhere.

Yes, in practice you'd often do this to force a specific source address
selection for that outgoing interface.  But this is another local policy
decision which should not be made default.


Bjørn