Re: [v6ops] Erik Kline's Discuss on draft-ietf-v6ops-cpe-slaac-renum-05: (with DISCUSS and COMMENT)

Fernando Gont <fgont@si6networks.com> Thu, 22 October 2020 15:20 UTC

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To: Erik Kline <ek.ietf@gmail.com>, Ted Lemon <mellon@fugue.com>
Cc: The IESG <iesg@ietf.org>, V6Ops Chairs <v6ops-chairs@ietf.org>, v6ops list <v6ops@ietf.org>, draft-ietf-v6ops-cpe-slaac-renum@ietf.org
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From: Fernando Gont <fgont@si6networks.com>
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Date: Thu, 22 Oct 2020 12:19:10 -0300
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Subject: Re: [v6ops] Erik Kline's Discuss on draft-ietf-v6ops-cpe-slaac-renum-05: (with DISCUSS and COMMENT)
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On 22/10/20 11:28, Erik Kline wrote:
> I agree.  I just think then the text about "the lesser of two lifetime
> values" doesn't quite read correctly nor give the impression that this
> applies to things like ULA prefixes.  I think it's probably pretty
> easy to fix with minimal text.

My shot at it:

At the end of this:

    CE routers SHOULD set the Router Lifetime to ND_PREFERRED_LIMIT.  CE
    routers SHOULD also set the PIO Preferred Lifetime to the lesser of
    the remaining preferred lifetime (see Section 3.1) and
    ND_PREFERRED_LIMIT, and the PIO Valid Lifetime to the lesser of the
    remaining valid lifetime and ND_VALID_LIMIT.

Add:

"If a ULA prefix is locally generated as specified in [RFC4193] and 
advertised on the LAN-side via PIO options, the corresponding PIO 
Preferred Lifetime and Valid Lifetime SHOULD be set to 
ND_PREFERRED_LIMIT and ND_VALID_LIMIT, respectively."



At the end of:

    CE Routers providing stateful address configuration via DHCPv6 SHOULD
    set the DHCPv6 IA Address Option preferred-lifetime to the lesser of
    the remaining preferred lifetime and ND_PREFERRED_LIMIT, and the
    valid-lifetime of the same option to the lesser of the remaining
    valid lifetime and ND_VALID_LIMIT.

Add:

"If a ULA prefix is locally generated as specified in [RFC4193] and 
employed for stateful address configuration via DHCPv6, the 
corresponding DHCPv6 IA Address Option preferred-lifetime and 
valid-lifetime SHOULD be set to ND_PREFERRED_LIMIT and ND_VALID_LIMIT, 
respectively.



Finally, for the DHCPv6-PD case, at the end of:

    CE Routers providing DHCPv6-PD on the LAN-side SHOULD set the DHCPv6
    IA Prefix Option preferred-lifetime to the lesser of the remaining
    preferred lifetime and ND_PREFERRED_LIMIT, and the valid-lifetime of
    the same option to the lesser of the remaining valid lifetime and
    ND_VALID_LIMIT.

Add:

"If a ULA prefix is locally generated as specified in [RFC4193] and the
  CE Router provides DHCPv6-PD on the LAN-side, it SHOULD set the DHCPv6
  IA Prefix Option preferred-lifetime to ND_PREFERRED_LIMIT, and the
  valid-lifetime of the same option to ND_VALID_LIMIT."


Thoughts?


P.S.: Bottom-line is that this is only special for ULA prefixes that are 
*locally* generated, since in that case there's only one lifetime 
involved (no "lifetimes" from the upstream).

Thanks,
Fernando




> 
> On Thu, Oct 22, 2020 at 7:11 AM Ted Lemon <mellon@fugue.com> wrote:
>>
>> I think it’s reasonable to assume that in some situations a ULA will be generated and not remembered, or that the /48 will be remembered but the subnetting will not be. E.g. this could happen in an HNCP-delegated network pretty easily. The set of behaviors we are seeing in existing border routers fairly constrained with respect to what is theoretically possible and even reasonable.  So I don’t think there’s a good reason to suggest different treatment for ULAs.
>>
>>> On Oct 22, 2020, at 01:37, Erik Kline via Datatracker <noreply@ietf.org> wrote:
>>>
>>> Erik Kline has entered the following ballot position for
>>> draft-ietf-v6ops-cpe-slaac-renum-05: Discuss
>>>
>>> When responding, please keep the subject line intact and reply to all
>>> email addresses included in the To and CC lines. (Feel free to cut this
>>> introductory paragraph, however.)
>>>
>>>
>>> Please refer to https://www.ietf.org/iesg/statement/discuss-criteria.html
>>> for more information about IESG DISCUSS and COMMENT positions.
>>>
>>>
>>> The document, along with other ballot positions, can be found here:
>>> https://datatracker.ietf.org/doc/draft-ietf-v6ops-cpe-slaac-renum/
>>>
>>>
>>>
>>> ----------------------------------------------------------------------
>>> DISCUSS:
>>> ----------------------------------------------------------------------
>>>
>>> [ section 3.2 ]
>>>
>>> * I absolutely agree in principle at these other lifetimes should be updated
>>>   to the shorter of the two applicable lifetimes, but I'm worried that this
>>>   text is not sufficiently precise.  Specifically, this recommendation only
>>>   applies to options that depend in any way on the change in the delegated
>>>   prefix, yes?  Perhaps just this qualifier is sufficient?
>>>
>>>   For example, none of these comparative lifetime recommendations apply to
>>>   a stable ULA for a router that meets requirements ULA-[1..5] and chooses
>>>   to advertise a ULA /48 RIO and maybe even a ULA DNS server, I think.
>>>
>>>   That being said, should this document also be saying that the ULA-derived
>>>   options SHOULD prefer the ND_{P,V}_LIMIT lifetime values, in case a reboot
>>>   causes a new ULA to be generated (i.e. the one supposedly in stable storage
>>>   is lost or otherwise unrecoverable)?
>>>
>>>
>>> ----------------------------------------------------------------------
>>> COMMENT:
>>> ----------------------------------------------------------------------
>>>
>>> [[ comments ]]
>>>
>>> [ section 3.1 ]
>>>
>>> * With respect to the second bullet: the lifetimes need to be dynamically
>>>   *updateable*, not necessarily updated if, for example, the ND_{P,V}_LIMIT
>>>   values are always lower than the remaining PD lifetimes.  In this situation,
>>>   the requirement is still that the lifetimes can be updated, but to the
>>>   casual observer of the steady state the RA contents might appear static
>>>   (e.g., while the PD'd prefix is continuously renewed).
>>>
>>>   Maybe there's no text required here, but I didn't want a reader to be left
>>>   with the impression that no two RAs could be identical
>>>
>>>
>>> [[ nits ]]
>>>
>>> [ section 3.3 ]
>>>
>>> * In the 2nd bullet's 2nd bullet (this might be easier if these lists were
>>>   numbered), it might be good to clarify that "the *deprecated* prefix can
>>>   simply be advertised..."
>>>
>>>
>>>
>>> _______________________________________________
>>> v6ops mailing list
>>> v6ops@ietf.org
>>> https://www.ietf.org/mailman/listinfo/v6ops
> 


-- 
Fernando Gont
SI6 Networks
e-mail: fgont@si6networks.com
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