Re: [dhcwg] Please review version -07 of draft-ietf-dhc-dhcpv6-stateful-issues

[神明達哉 <[e-mail]>]

At Thu, 16 Oct 2014 18:13:30 +0000,
"Bernie Volz (volz)" <[e-mail]> wrote:

> Well, what this was there for was to indicate that if there were no IAADDR/IAPREFIX options or the lifetimes were all 0, the "effective" T1 (and T2) for this IA_NA or IA_PD would be 0 and we would NOT want to use that. If the "effective" T1 is 0, we want the client to skip that set of T1/T2 values.
>
> In this case, the server would have had to send 0 not because it didn't calculate the T1/T2 values, but because that is what the values are. But the client is told that if these values are 0, it needs to calculate them (from the lifetimes in that IA). Thus the resulting ("effective") values are 0 too. And we don't want the client to Renew/Rebind immediately?

To be accurate: "if these values are 0", the client can send next
renew at any timing (slightly different from "the client is told to
calculate it") per Section 18.1.3 of RFC 3315:

   If T1 or T2 is set to 0 by the server (for an IA_NA) or there are no
   T1 or T2 times (for an IA_TA), the client may send a Renew or Rebind
   message, respectively, at the client's discretion.

And, since it's up to the client how to calculate the value, the
"effective" value is not necessarily 0.

Obviously, we wouldn't want immediate (and repeated) renew/rebind if
the calculated value is somehow 0.  RFC 3315 is just silent about
these corner cases, and in my understanding it's left to implementor's
choice.  In a DHCPv6 client I'm relatively familiar with, it sets T2 to
30 (sec) and T1 to 18:

        /*
         * Be proactive for too-small timeout values.  Note that
         * the adjusted values may make some information expire
         * without renewal.
         */
        if (ia->t2 < DHCP6_DURATION_MIN) { /* DHCP6_DURATION_MIN=30*/
            ia->t2 = DHCP6_DURATION_MIN;
            ia->t1 = ia->t2 * 5 / 8;
        }

Anyway, these are minor technicality in this context.  As I said
in my previous message, I'm okay with any sensible and clearly-written
behavior since the basic assumption is T1/T2 and lifetimes should be
same for all IAs and other cases are exceptions.  I just tried to say
that the current text of the draft is not clear enough.

--
JINMEI, Tatuya