Subject: IPv6 Scoped Address Architecture (RFC 2710)

From: "Narsimharao Nagampalli" <[email-masked]>
Date: Tue, 18 Jul 2000 05:51:02 -0600

Hi,

In the RFC (2710) on the scoped address architecture, we seem to consider scenarios where source address can be smaller scope than the destination address. I have two concerns regarding the same and also would be interested to know of scenarios where such a feature is useful.

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.

Any comments/Insights?

Thanks and Regards
Narsi

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From: "Narsimharao Nagampalli" <[email-masked]>
Date: Tue, 18 Jul 2000 06:28:58 -0600

I am sorry, I referred a wrong RFC Number. It was the draft on IPv6 Scoped Architecture.

Regards
Narsi

>>> "Narsimharao Nagampalli" <[email-masked]> 07/18/00 05:21PM >>>
Hi,

Fragmentation

Flow Label

Any comments/Insights?

Thanks and Regards
Narsi

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From: "Narsimharao Nagampalli" <[email-masked]>
Date: Tue, 18 Jul 2000 22:33:17 -0600

Steve,

Thanks for the clarificaiton and I totally agree that the behavior explained in section 9 would avoid the issues I have mentioned.

But,  following is a reference from section 7 (last paragraph of the section) of the draft which has got me confused.

" One possible reason for such behavior is that the source
   address chosen by the upper-layer is of smaller scope than the
   destination, e.g., when using a link-local source address and a
   site-local destination address.  "

Thanks and Regards
Narsi

>>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: Brian Zill <[email-masked]>
Date: Tue, 18 Jul 2000 22:03:25 -0700

Hi Narsi,

> But,  following is a reference from section 7 (last paragraph 
> of the section) of the draft which has got me confused.
> 

You can legitimately form a packet where the source address is of a smaller
scope than the destination address.  Due to the forwarding rule of section 9
that Steve noted, this packet will only get to the destination if it resides
in zone of the smaller scoped address.  For the example above, this packet
with the link-local source address will get to its destination if (and only
if) the site-local destination resides on the same link.  This allows a node
that only has a link-local address to talk to other nodes on its link even
when it only knows their site-local addresses.  Granted, this example will
probably be rare.  But the same applies for sending from a site-local source
address to a global destination.  You want the communication to succeed if
the global address resides in your site.  And the forwarding rules will
cause a router to drop the packet (and send an ICMP message back to the
sender) if it tries to leave the site.

Hope this helps,
--Brian