Subject: Re: IPv6 Scoped Address Architecture (RFC 2710)

From: Steve Deering <[email-masked]>
Date: Tue, 18 Jul 2000 09:12:22 -0700

At 5:51 AM -0600 7/18/00, Narsimharao Nagampalli wrote:
>Fragmentation
>One concern is regarding IPv6 fragmentation. There we use the source address followed by a unique ID generated at the source to define a fragmentation sequence. Now, consider the case where two link local addressed sources are sending fragments to a site-local address and happen to use the same ID's. I can not see a way in which the destination can re-assemble these two train of fragments properly.
>
>Flow Label
>Same issue like fragment ID. Flow label ID and Src address again are used together to identify a flow. In the above scenario again, there could be issues in distinguishing across flows.

Narsi,

A packet is not permitted to leave the zone of uniqueness of its source
address (see section 9 of the scoped architecture draft, second bullet),
so your example problems ought not to arise.

Steve

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From: JINMEI Tatuya / 神明達哉<[email-masked]>
Date: Fri, 21 Jul 2000 22:07:57 +0900

>>>>> On Tue, 18 Jul 2000 09:12:22 -0700, 
>>>>> Steve Deering <[email-masked]> said:

> so your example problems ought not to arise.

Correct, but I recall another (or a related) issue triggered by the
original question. Consider the following topology:

nodeA-----------------nodeB------------------nodeC
    fe80::1    fe80::2     fe80::2    fe80::1

This is valid if the link between A and B is different from the link
between B and C.

Then suppose that nodeA and nodeC are sending fragmented packets to
nodeB using a same fragment ID at the same time. A poor implementation
would be confused when reassembling the packets.

So, implmentations should care the zone of received fragments as well
as the source and destination addresses (and fragment ID) when
reassembling.

This may be a trivial requirement and needs not to be documented,
though.

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