Re: [dhcwg] Re: PD lifetimes

>>>>> On Sat, 25 Jan 2003 06:46:26 +0100 (CET), 
>>>>> Erik Nordmark <Erik.Nordmark@sun.com> said:

> Presumably the PD draft could do this as well by having a bit (or two)
> indicating wheter the lifetime(s) should decrement in real time or be
> constant.

> Would that make sense?

Yes, *if we want to allow the delegating router to have the ability to
control the downstream valid and preferred lifetimes*.  Actually, RFC
2894 (Router Renumbering for IPv6) has a similar notation:

   V           A 1-bit flag indicating that the valid lifetime of the
               New Prefix MUST be effectively decremented in real time.

   P           A 1-bit flag indicating that the preferred lifetime of
               the New Prefix MUST be effectively decremented in real
               time.
(Section 3.2.1.2)

The current PD draft implicitly assumes the (not-yet-introduced)
additional flags are on, while these bits are off in the current
typical cases.

Before going that further, however, I still think it is overkilling
for the delegating router to have the ability to control the
downstream lifetimes.  IMO, the requesting router (and the site's
administrator) should be responsible for such parameters, with one
trivial constraint: the site lifetimes must not be smaller than the
lifetimes of each downstream link.

In summary,

I first would like to make a consensus if we need to allow the
requesting router to have the ability to control the downstream
lifetimes.  As I said above, I'm negative on this.

If our consensus is to allow the delegating router to have the
ability, it's okay.  Then,

  1. the requesting router should also have the additional bits (like
     P and V above),
  2. (this may be controversial) the lifetimes in router advertisement
     on each downstream link should be the same as the default of RFC
     2461 (i.e. AdvValidLifetime and AdvPreferredLifetime, NOT
     decreasing in real time), as long as Renew/Reply exchanges
     succeed, and
  3. in any case, the valid lifetime of a prefix delegated by PD must
     not be smaller than the valid lifetime in router advertisements
     on any downstream link.

Note that, as a consequence of 2 and 3, the default value of the valid
lifetime in a PD prefix option must be larger than AdvValidLifetime.

					JINMEI, Tatuya
					Communication Platform Lab.
					Corporate R&D Center, Toshiba Corp.
					jinmei@isl.rdc.toshiba.co.jp
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