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

From: [email-masked]
Date: Mon, 28 Oct 2002 20:32:42 +0530

It has been mentioned in draft section 11.3.3, that

" The mobile node SHOULD further limit the lifetimes that it
sends on any Binding Updates to be within the remaining
preferred lifetime (see Section 10.9.2) for the prefix in its
home address.

These limits on the binding lifetime serve to prohibit use of
a mobile node's home address after it becomes invalid. "

The only reason for tracking preferred lifetime should be to
avoid post invalidation at MN's end, considering the
propagation delay.

Is there any other reason, for tracking preferred lifetime of
Home addresses?

As per IPv6, it is sufficient if the nodes keep track of valid
lifetime, since preferred lifetime is less than or equal to
the valid lifetime.

By this, are we limiting the address usage at MN only till
preferred lifetime.

But at HA's end, HA keep's track of valid lifetime. Is there,
any possibility of inconsistency creeping in.

Thanks,
Srinivasan.D

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From: Jari Arkko <[email-masked]>
Date: Mon, 28 Oct 2002 18:18:49 +0200

> lifetime, since preferred lifetime is less than or equal to

I don't think IPv6 RFCs 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.

So I think we are safe if we pick the smaller one of the lifetimes
to track. And this is what we do today. Or have I missed
something?