Subject: [Int-area] Re: [netlmm] Multilink Subnet Considerations for NETLMM Addressing

From: Julien Laganier <[email-masked]>
Date: Fri, 1 Sep 2006 09:19:44 +0200

On Thursday 31 August 2006 19:55, James Kempf wrote:
> Maybe I'm confused, but I don't see what L=0 really means. If
> ADDRCONF assigns the prefix to the interface, then the prefix is on
> link for at least one node, the node that configured the interface
> with the prefix. I suppose one could argue that, even if that node
> considered the prefix on link, that node should not assume another
> node does. But IFICT, 2461 doesn't have specific, RFC 2119
> requirements language around that.
>
> If M=1, and stateful configuration is used, then I could see some
> sense in L=0, since I assume in that case the prefix is not
> assigned to the interface.
>
> Can anybody say what real implemetations do with this?

BSDs sends packets to the default router.

--julien

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---

From: JINMEI Tatuya / 神明達哉<[email-masked]>
Date: Mon, 04 Sep 2006 17:28:15 +0900

>>>>> On Thu, 31 Aug 2006 14:16:47 -0700, 
>>>>> "James Kempf" <[email-masked]> said:

> No, but I think it would be worthwhile to find out what real implemenations 
> do.

As replied in a separate message (not from me), BSDs separate the
processing of an RA prefix wrt address configuration from the
processing of the prefix wrt on-link determination.

Specifically,

A. if a BSD host receives an containing prefix P/x with the L flag
   on, it installs a direct route P/x to the receiving interface,
   indicating Neighbor Discovery (NS/NA) is necessary for destinations
   covered by the prefix.
B. if a BSD host receives an containing prefix P/x with the A flag on,
   it configures the interface with the address P:I (I is some
   interface identifier)

A and B are done separately and independently, and processing B does
not involve any direct route creation.

So, if a BSD host receives a prefix P/x with the L flag off and A flag
on, it configures the receiving interface with the address P:I/128.
Since there is no direct route for the prefix P/x, any packet to
destinations covered by the prefix (except P:I) will be sent to the
default router (if any).

> Unless an IETF standard has specific RFC 2119 languge in it, your milage 
> can vary.

That is true in general, and it's not specific to RFC2461 (or
2461bis).  The semantics of the L bit might be clearer, but I
personally believe the L bit processing is widely interpreted as
described above.

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