Re: [v6ops] A common problem with SLAAC in "renumbering" scenarios

[神明達哉 <[e-mail]>]

At Wed, 27 Feb 2019 03:45:00 -0300,
Fernando Gont <[e-mail]> wrote:

> >> > while we cannot completely ignore non-compliant implementations (if
> >> > any) in practice, IMO the existence of violators shouldn't be the
> >> > primary reason for tweaking the protocol.
> >>
> >> Which specific tweak are you referring to?
> >
> > Changing the default value of AdvPreferredLifetime and
> > AdvPreferredLifetime currently defined in in RFC4861.
>
> The rationale for that it's what's in the I-D, namely:

To be clear, I didn't oppose to the idea of this change.  I just
pointed out that the existence of buggy "script" didn't seem to be
a convincing reason for the change.  My interpretation of this message

https://mailarchive.ietf.org/arch/msg/ipv6/Fa89c-WmpEzBFqnpcZQsTZ5q2Z8

is that it's in the context of changing the default value of
AdvPreferredLifetime and AdvPreferredLifetime, referring to the
DHCP-PD CPE case.  Ole pointed out it's a red herring, and you
responded to it as:

>> They should. However, quite frequently the DHCPv6-PD part is a different
>> piece of software from the ra{d,dvd} part. Both pieces are glued by some
>> script, and the lifetime is *not* dynamically adjusted.

This looked to me like that we should consider changing the default
AdvXXXLifetimes because of this (buggy) piece of software.  It didn't
make much sense to me, hence my comment.

> > first place or they shouldn't change the delegated prefix.  I'm not
> > saying this to argue there's nothing we can/should do for such a broken
> > operation.  But this case seems weak as a justification to change the
> > default lifetime values in RFC4861.
>
> The justification is noted above.  Regarding "broken operation"... the
> survey referenced in our I-D notes that 37% of the surveyed ISPs do
> dynamic prefixes. Blaming the ISPs is not really going to improve user
> experience...

I don't think we are on different pages regarding "blaming the ISPs" -
see my second sentence above.  It's all about whether that can justify
changing a particular part of the protocol.

BTW, in the original context of changing the default of
AdvXXXLifetimes, it wouldn't help anyway against the mixture of broken
ISP operation and buggy piece of software: regardless of the protocol
default, that piece of software would simply copy the delegated prefix
lifetimes and keep using them.

--
JINMEI, Tatuya