Re: Understanding IPv6-PD over PPPoE



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


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