Subject: RE: reconnecting an interface

From: Richard Draves <[email-masked]>
Date: Fri, 15 Oct 1999 14:59:12 -0700

> 	You may want to take a look at KAME nomadic node hack by Tatsuya
> 	Jinmei, which is described in section 3.4 of the 
> following paper:
> 	http://www.isoc.org/inet99/proceedings/4s/4s_2.htm
> 	The code is available in normal KAME distribution and 
> works well.

I worry that there could be an accumulation of detached prefixes and
addresses...

It's not clear to me what happens to UDP/TCP sockets that are using an
address that becomes detached?

The paper says: "One simple solution to these problems is to force the node
to discard the old prefix and the old address after moving. But this
approach may cause an unexpected deletion of prefixes and addresses that
should remain valid. For instance, suppose that there is a failure of the
router on a network while a laptop computer is suspended. When the laptop's
operation is resumed, it should discard the prefix and the address that were
advertised before suspension, because there is a possibility that the laptop
has moved from the network. The laptop, however, cannot get a prefix anymore
because the router has already stopped; it therefore fails to communicate
with any nodes, even with those within the network."

So the problem is that the router's down, so communication fails. That
sounds like expected behavior, why is it a problem to fix?

Rich
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From: Bill Sommerfeld <[email-masked]>
Date: Fri, 15 Oct 1999 18:58:01 -0400

> address that becomes detached?

Ideally nothing, because someone could have tripped over the LAN cable
or the hub's power cable and it should all come back once I notice the
failure and plug it back in.  

> sounds like expected behavior, why is it a problem to fix?

The laptop should still be able to talk to other nodes on the same
subnet even if the router's down, but it may only know them by their
global address rather than their link-local address..

					- Bill

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From: JINMEI Tatuya / 神明達哉<[email-masked]>
Date: Wed, 20 Oct 1999 17:52:54 +0900

I'm sorry, I should've answered your questions but I've not had enough
time.

>>>>> On Fri, 15 Oct 1999 14:59:12 -0700, 
>>>>> Richard Draves <[email-masked]> said:

> address that becomes detached?

A detached address is not used as a source address of a "new"
connection, but it's still valid in a bound socket (just as a
deprecated address). So if the detached address is luckily valid
(i.e. can be effectively used for a communication) after moving, the
socket will simply be able to continue to use the address.

> sounds like expected behavior, why is it a problem to fix?

As Bill has already answered (thanks!), my concern here is a case
where another node on the link tries to connect to the laptop using
the (mistakenly) discarded address.

I admit, however, that it's not a typical case and that the network
can't be expected to work normally when the only router is
down. Anyway, we've already implemented the approach and the
implementation has worked fine for more than one years for typical
cases as well as for rare cases.

					JINMEI, Tatuya
					Communication Platform Lab.
					Corporate R&D Center, Toshiba Corp.
					[email-masked]
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