Subject: Re: [mobile-ip] Tracking preferred lifetime of Home addresses

From: [email-masked]
Date: Tue, 29 Oct 2002 11:02:01 +0530

Jari Arkko wrote:
> I don't think IPv6 RFC's explicitly say what to track (or can pinpoint
> the RFC and section)? But it seems to me that you'd have to track
> preferred lifetime as it is smaller. Note that section 12 of RFC 2461
> says one should track valid lifetime, but that is in a context where
> renumbering has occurred and a node which hasn't been on for
> a long time gets back to the network. There it is necessary to
> announce zero lifetime as long as the valid lifetime, because
> otherwise the node might think the prefix is still valid.

Yes, indeed I was referring to the same section of RFC 2461. As far as I
know, the idea of splitting address lifetime into preferred and
deprecated is only to aid in renumbering.

In section 4.1 of RFC 2462, it is mentioned that
"  Dividing valid addresses into preferred and deprecated categories
   provides a way of indicating to upper layers that a valid address may
   become invalid shortly and that future communication using the
   address will fail, should the address's valid lifetime expire before
   communication ends.  To avoid this scenario, higher layers should use
   a preferred address (assuming one of sufficient scope exists) to
   increase the likelihood that an address will remain valid for the
   duration of the communication.
   The deprecation period should be long enough that most, if not all,
   communications are using the new address at the time an address
   becomes invalid. "

The only difference is, in MobileIPv6 due to renumbering the
communications will abruptly break at MN's end, since we are tracking
preferred lifetime. Whereas IPv6 allows communications to continue till
the valid lifetime, even after deprecation.

Is this, the desired one?

Regarding the inconsistency I was talking about i.e HA tracks valid
lifetime and MN tracks preferred lifetime, I would like to give an
example :

Assume MN has 3 Home addresses and it has registered with HA by sending
a BU with 'S' bit = 0. HA creates BCache entry for all 3 Home address.
Now, one of the address is getting removed, so they deprecate the
address and send an MPA. Upon receiving the MPA, MN removes this
address from its list of home address.

Does it need to send a separate BU for this Home address for deletion?

If yes, then BCache entry for this home address will be deleted at HA's
end also.

Still, lets consider this HA is down immediately, so MN tries and
registers with another HA with a BU with S bit = 0.
HA creates BCache entries for all Home address of MN including the
deprecated one. HA will tunnel these packets, but they will be dropped at
MN.
But for MN, this address is no more a Home address.

Ofcourse, these address will get invalidated after the deprecation time.
But this behavior will exist till the deprecation time.

Thanks,
Srinivasan.D

---

From: Jari Arkko <[email-masked]>
Date: Tue, 29 Oct 2002 17:18:57 +0200

> Is this, the desired one?

Hmm... OK, I think you are right. We need to say valid lifetime even
in the mobile node side. Document changed. New issue #152.

Jari